I don't think it's unfortunate at all. You are comparing an isometric sprite based game vs a full 3D experience.
With tech being the way it is today, a game company could easily pump out 2-3 games like Fallout, Fallout 2, and Fallout: Tactics a year due to the ultra low tech requirements. For a full 3D experience like Fallout 3 takes a LOT more time and money.
It probably isn't that simple. Different generations of software have always had different obstacles to overcome. For example back then memory had to be conserved much more carefully, for example radio stations as those are in FO3 would have been way out of league for original games, just when it comes to running memory, disk space is whole different ball game. 233mHz PentiumMMX with 32meg ram was high end when games were developed, if win95 took something like 10megs and running game itself took 20 megs, it doesn't leave much room for cached music. All sorts of stuff that comes now with DirectX had to be coded to game itself. Much easier to use development tools have made life of map designers much easier, same applies to guys who make creature models or even textures. Back in the day they couldn't spare few hundred polygons due to memory limitations. Full 3d experience itself isn't worth much if content is pointless, it is very much like saying that Aliens Vs Predator is better movie than either Alien or Predator as it has better special effects.
However, the sales of all three games like that wouldn't even scratch the surface of the profits of a game like Fallout 3. Gaming companies today MUST have as wide a target demographic as possible. The shareholders will not appreciate a game that only sells to a small hardcoe niche.
When it comes to sales... market itself is whole lot bigger than it was ten years earlier. Think about launch sales of current generation consoles and compare that to sales of previous generations launch sales. There much larger potential market available now.
Casual vs hardcoe audiences is quite valid point, but taking so called HC product and dumbing it down to casual might create abomination that doesn't serve anyone's interests. Pretty much everything is compromise at some level, but those compromises have to be made at right places. Fallout 3 does job pretty well, but it fails plenty of those, especially when it comes to being RPG. In my opinion it has too much political correctness and it underestimates players capability to think and solve problems. Game mechanics are rather mediocre and in some cases illogical, like repair being most important combat skill. Game mechanics of originals were also flawed. Reasons why original Fallouts were different from average RPG of that time was freedom of choices combined with consequences of those choices, that is basically principle failure of Fallout 3. Freedom action isn't only about big map and lot of places to explore. Freedom comes with price tag, that is responsibility. In FO3 player doesn't have to pay for their sins, they cannot even commit that sin due to potential offensiveness of those actions.