Probably because the entire lot of them as above said they were attention grabbers for new systems.

BUT...

I think there is an even larger reason. General stupidity and complacency. Take both Project64 and 1964 for example. Each has a strong backbone but are useless with out plugins. These plugins sadly are limiting and can only go so far. PJ64 1.5 had a good year or so lead over 1964 0.99 release from a year ago. 1964 claimed it would be the best, yet they lied and just bet the farm off the stupid RICE plugin. If you inject the plugin into PJ64, both run all the same shit just as well as the other does.

Disgusting no?

This is an issue with both the N64 and PSX and sadly I doubt unless someone who is not incompetent shows up to correct the problem and makes a full on non-plugin bullshit emulator for either system it will never get any better.