Maybe there used to be more diversity and innovation, back when production costs were much lower?
Game developers still appeared and disappeared at a regular rate, but there were so many more the smaller ones.
Maybe games have become too serious a business, going the way of Hollywood (i.e. taking themselves too seriously)?
I asked a similar question a while ago in a different place, why I haven't seen a racing game that I really liked since Carmageddon.
They may be all realism simulators today, but the fun has gone out of them
Anyway, if you like HoMM3 then you have to give Disciples II a try. Beats HoMM3 in just about every aspect. And the gold edition is dirt cheap right now from Strategy First's homepage