I think the point is Neil, as with any purchase of any item, part of it is the immediate 'buy me now' appeal. Sometimes, there is a 'want' to build the particular kit straight away, and sometimes it's bought for future projects. As for purchasing one 'the next day', sadly, that is no longer always true. The days of kit manufacturers having a seemingly endless catalogue of products, always in stock year in year out, are long gone. Kits seem to be around for a limited period, then withdrawn, sometimes not re-appearing on the shelves until many years later, often at very inflated prices. I've lost count of the times when I've planned a series of builds, for example, Battle of Britain aircraft, with the intention of buying a kit, or kits, at 'sometime', only to find they are no longer available, often for many years, often never.
Now, if or when I can afford it, I'll buy a kit for a project which might not come to fruition for many years, my '56 Squadron' collection being a good example, rather than find the overall project has stalled due to lack of suitable kits.
Although I tend to agree that a huge 'stash' of kits may seem a bit strange, personally, I only ever have around 20 or so kits in stock at any one time, and some of those have been given to me as gifts, and will eventually be built.
There are certainly stranger, and harder to explain, collections of items on this planet, so I don't believe that an individual's 'stash' is any thing out of the ordinary, especially if the ultimate intention is to build them.
It's a hobby, and, for those who partake, it provides many things, from relaxation, the sense of achievement and satisfaction, to learning more about a period of history and the technology of the time.
I can think of a few 'hobbies' which cost a darned site more, without providing all of the above.