The real issue isn't the ability to DO it ... the issue is constantly-shifting goals and specifications. I'd describe it, but people like FlyboyJ and Drgondog have lived it like I have and KNOW the problems caused by constantly shooting at a moving target. There are many others in here who have lived it and know, too.
This same sort of problem develops with nearly any sort of engineering. I can think of some horribly organized civil engineering and development plans that either ended up getting re-evaluated and canceled outright or (in the case of the new High School that finally opened around 10 years ago) finally put back on track after months or years of varying delays and political/bureaucratic messes. In some cases it's changing requirements in other cases it's improper planning/data collected and provided by the customer (government/military in these cases) or upper management in the case of internal R&D projects (... or management influenced by 'market research' and marketing divisions ... ). Middle management of some sort or another that lacks the skills to properly plan and deliver the requirements in the first place and also usually lacks the understanding of engineering or economics to minimize wasteful spending and delays forced my belated amendments to requirements. (or, of course, cases where they DO understand but just don't CARE about doing their job well, and only care about looking good playing political/bureaucratic games)
Same goes for tons of stories I know in the computer and electronics industries, though not too many specific to military contracts. (probably because people tend to be less free to openly discuss those matters ... or just because the consumer market is an even bigger mess than the military/government one)
All too rare do you get politicians or corporate bureaucrats that know how to play the game well AND actually care about getting things done right ... and are good at doing both while not looking underhanded or sneaky about it to the public.
Hmm, I suppose the more practical public image problem is just that a lot of people find it much easier to focus on short-term costs and end up being penny wise and pound foolish with lack of foresight or concern for long term costs. (monetary and just general consequences)
The government wastes a LOT of time and money trying to get contractors to pay for things that have to be redone at government request due to government-specified changes. They wind up paying anyway, but they drag you through the mud to get paid.
And waste a ton of time and money (and other resources) bickering about it rather than just settling for some compromise to expedite things. But then you need at least one side to actually be willing to compromise and unless you have BOTH that tends to mean the more sensible one eating the entire cost just to avoid delays and waste. Then again, if both sides were being sensible and rational about the entire project, they likely wouldn't be running into those sorts of delays and conflicts nearly as often either.
While I was at one company, we had local machine shops refusing to deliver fixtures until they were paid for because the money was slow in coming. Naturally, that impacted schedules, which tended to draw penalties on top of schedule slips ... all due to inefficiency in accounts payable. Our company refused to finance government projects and wait for the payment to come in the mail, so it was hurry up to get it done on time and then wait around to get paid before continuing with the supposed "continuous-effort" project.
As a taxpayer it was outrageous. As an engineer it was business as usual on some projects that shall remain nameless.
That all sounds very familiar, and delays tend to be compounded ... everything's great when it goes to plan, but with lack of margins for error and contingencies for mistakes/changes you end up with cost overruns ... investors/buyers being unwilling to pay more or other bottlenecks for procuring added resources to keep up pace and end up in a vicious cycle of overlapping costs. Developers that under-bid costs to win a contract would make that problem worse too. (speaking in general, not saying there's any relevance to the F-35's case)
The issue is the CUSTOMER is inducing the changes!!!!
You know, that really is the bigger issue even beyond the mistakes in planning that leads to improper requirements in the first place, especially since you COULD end up with a very good, solid plan and resulting specification that made perfect sense for the overall requirements but added changes being thrown in for stupid reasons after the fact due to shifting politics or management.
That, and curbing excessive changes and wasteful spending (and delays ... and resulting further waste) resulting from that might be a lot more practical to actually moderate than applying quality assurance techniques to the planning stage itself. Say if Congress really wanted to cut the budget, moderating THOSE sorts of situations might make a lot more sense ... the problem would still be: who actually intervenes there? Unless you have people in the government who actually have at least a basic understanding of the engineering and economic issues (and the concepts associated with good quality assurance) involved and are actually focused on expediting development and minimizing wasteful spending you're stuck where we already are. (it seems like there's a LOT more engineers with a decent understanding of politics than there are politicians with decent understanding of engineering ... and lack of any sort of coercion compromising their integrity)
It's almost like we could use some sort of quality assurance oversight committee to arbitrate in such matters. (any added costs there would probably be far less than the wasted time/money on mismanaged projects, the problem would be actually establishing a group like that and maintaining the competence and integrity of the committee members) Plus, if the DID do their job well ... they'd probably end up dumped on by the media and politicians ... people tend to not like compromise or being told they're 'wrong' ... and quality assurance very often requires telling ALL sides they're wrong at some point or another. It's the whole non-partisian political problem. (I'm getting far afield here, but I can't help but be reminded of some of the same political and economic issues Teddy Roosevelt ran into in office or during the 1912 election)