It's supply and demand in operation. Outside of Soviet/ Eastern Bloc stuff, there's little available in wholesale quantities anymore. As an example, Bren guns were relatively cheap 5-10 years ago as a large quantity had been imported from Greece. They're now all gone and Bren prices are climbing steadily. The 'good old days' of various desirable WWI / WWII British
, German
and US guns being plentiful and relatively cheap are long gone and probably won't return
As for requiring pre-95's to be redone, it was an idea posited in a Home Office committee report last year, but as far as I'm aware it hasn't gone further. As there's no register of who owns what, the scope for creating a black market is obvious.