I disagree with point 2, but point 1 is fair. Money. It costs a small fortune to make a good game, thanks in part to the massive graphics boom we had. But look at Jerykk's list: many of those games didn't sell enough to recover their costs back then. Now increase the development costs by a factor of 10...
As for 10 year old gameplay being fun... not really. A classic might still be a classic (and it might not be, as some games are not as fun to return to. Case in point: I76, which feels like a lame 2D WWI/II sim, which it pretty much was. With the Y axis removed it was endless circling and leading. Or look at how little fun virtually every NES game is.)
But Doom 3 had 10 year old gameplay. And monumentally sucked.
Quake 4 had 10 year old gameplay. And monumentally sucked.
Very little from back then can be cloned directly and still be fun.
Many people here constantly forget that, looking back with a combination of rose-colored glasses now and rose-colored glasses then (as you were younger and less cynical.)
Most of the games from 10 years ago were completely awful.