CO said:

Why didn't the Beatles continue making music together after 1970 up until John Lennon's death in 1980?

Because they couldn't get along anymore, couldn't write together anymore, couldn't decide which songs they wanted on an album anymore, didn't like each others' wives, didn't really like each other anymore, and their financial & management problems with Apple Corps. Leaving a respected legacy was the least of their concerns.

*edit* ^ Sorry, I see that was already addressed by Frink.

Regarding the tainted legacy\decreased enjoyment of the past factor; I see both sides (I'm a cubist). The legacy of Star Wars was tainted a long long time ago (marketing tie-ins & Return). If the films would have been good, I wouldn't really care too much. However - they were crap, so I let nearly all of it go (actually all of it for about 12 years). So in that respect, I did let the present (at the time) affect the past.

I eventually ignored all the ridiculousness and went back to the only story that had ever really moved me, Star Wars77.

That said; I have grown somewhat tired of the 1977 story again and at least a touch of that is the way the franchise is now being handled\tainted\weakened\developed\falsified\viewed\suppressed\etc. However, it's mostly because I want more story & depth than just the Star Wars77 story.