1. It's plainly impossible to make a game with hundreds of levels (like Skweek, some versions of Gauntlet/Boulder Dash) or a huge map (Might and Magic, Ultima IV) if each level needs its own textures, 3D design, ambient sound and whatnot. Therefore, it's very difficult to make long games.

2. Most people (including myself) don't like hard and short games: hard games have to be long in order to entertain, getting stuck in a certain point is usually not fun (unless if the game is a masterpiece like early Sierra adventures). So, if it's difficult to make long games, it's also difficult to make hard games. That's why most modern games are irritatingly easy. (Severance, Tomb Raider).

3. Even if hard games weren't so difficult to code, they wouldn't release a lot of them anyway. They have spent their money in making the "outro" video, so they actually want you to see it. Some old arcade games were impossible or almost impossible to beat (i.e. Gauntlet and Arkanoid, which took me years) and their outros were nearly inexistent.

4. Old games were many times made by a single coder, or at least a single person had the idea and others put it into practice. Now, games are made by huge teams hired by multinational enterprises. And, as Descartes said when video games didn't yet exist,

"Thus it is observable that the buildings which a single architect has planned and executed, are generally more elegant and commodious than those which several have attempted to improve, by making old walls serve for purposes for which they were not originally built."

Lord British, John Van Caneghem, Roberta Williams and Sid Meier are examples of what a "single architect" can do.

5. Some genres just weren't born to be 3-D. 3-D is good for some things (like racing games or first-person shooters), but totally spoils others. 3-D platform games completely suck. 3-D RPG's are sometimes good (Might and Magic VII), but a 2-D RPG can be just as good with less frills. The best combat games I have seen (Last Blade II...) are 2-D. Why do they release so many 3-D shit? It seems that the single word "3-D" sells copies. So the obvious conclusion is: we (or most of us) are dumb.

Long life to emulators.