I think a lot of hubris was involved. There seemed to be an attitude that we are so good we don't need to test we know it works.Testing, I'm guessing. The Mark 13 and 14 weren't tested because of expense.
Last I had heard, neither Thiokol (the contractor for the SRB) nor Rockwell (the builder of the Shuttle, and prime contractor for the STS) were government-owned enterprises. The Challenger Disaster was because of a design flaw (Thiokol's responsibility) compounded by a management culture at NASA which put schedule above all else.This whole experience with a government owned torpedo factory was such a delightful success that it was duplicated in the 1970's for something called the Space Shuttle, with similar results.
Interestingly, the German Navy also started WW2 with very poor torpedoes. The errors were totally different so that, for example, American torpedoes ran deep because the designers had forgotten Bernoulli's Principle and assumed that they were measuring the water depth from a stationary torpedo whilst the Germans assumed that they could balance the water pressure with air at atmospheric pressure in a tank but the tanks tended to slowly leak and the pressure in a submarine was higher when diving. One difference was that the German officers responsible were court martialled and imprisoned.