(1) I think it doesn't matter whether it's jets or prop-jobs, many of the manufacturers just tend to be wary of creating something 'different', because there often isn't the market for it.

With the jets, that tends to mean F15, F16, F18, F86 etc, just as with the pro-jobs you get a gazillion people doing the P-51.

(2) I also think that whenever the latest Jet_China_X shop starts up, they look at what is already selling well, and they say "We can largely copy that and take part of their market since we already know people want to buy that model and it flies well" ; Having the guts to do a completely different model means (a) extra financial risk ; (b) some market research ; (c) having to do some of your own R&D and (hopefully) test flying, manual creation etc. That puts a lot of companies off either because they don't want to take on htat work / risk at all, or because they are wary that once they take it on someone else will largely copy their model and be able to sell it cheaper due to not having those costs.

So, when you DO find someone doing something a bit different, remember to thank them !