There's a reason why "jumping the shark" is a trope. No matter how popular and compelling something might be, there's always a point of diminishing returns. Once you've trashed a franchise, it's very difficult to rebuild; If you end on a high note, you leave the audience wanting more.
Rick Berman and Brandon Tartikoff saw what was being attempted with Babylon 5 and recognised the future of television - deep, complex story arcs that span across seasons. They realised that while TNG still had some mileage left in it, they had an opportunity to use familiar elements in a new and exciting way. The results were, in my humble opinion, the absolute pinnacle of the Star Trek canon.
Yeah. Even while I'm deluged in an ocean of pretty dman good modern tv, I find myself throwing on an old episode of TNG from time to time. It's still a joy to watch.
There are plenty of folks who will read every book in endless genre series and complain when some favorite TV program gets canceled after 10 years.
Others like me are pretty much ready to move in from a series after 5 years or so no matter how good it is. I just lose interest.
It was the former fans that bright us TNG in the first place - constantly fighting for more trek throughout the 70s, to be rewarded with Trek's golden era from 87 onwards.
(I grew up watching TNG and love it, btw, fwiw, etc. etc.)