It being your fav doesn't change that the overwhelming response was incredibly negative and it resulted in the end of the B&B era & put both the film & TV franchises in stasis for years.
Some points.
First I read your post wrong I thought you were revering to "modern Era' trek, which is what I referenced, meaning Discovery forward.
Then to respond to your reply.
There is no data anywhere that supports the quality of the programming is what caused the continued decline of Trek's ratings (thus its ending) starting with mid season 6 of TNG and season 1 of DS9 that basically continued through DS9 run, through VOY run, and through Enterprise's run.
The comments on boards aren't and never have been a statistical sampling referencing the feelings or opinions of the general tv audience. Now quality can be a factor, but there are a host of things that can cause an audience to no longer follow a show. From death, competition, companion programming, to amount of tv a person consumes and how it changes through the events of their lives, to even factors like burnout, or how the visual style of story telling changes over time.
But one thing to ask yourself looking at the data especially once we got viewer numbers versus estimate viewer numbers based on HH data. Is that outside of each new show getting a boost with its pilot (and each pilot after DS9 getting a smaller and smaller sampling) is that if you honestly believe quality was the primary factor it means every earlier season was better then the next, and I doubt many actually feel that way.
Take two fairly well liked German era shows, TNG and DS9. Using ratings (the only statistical sampling we have on Trek) season 7 should be liked more then season 3, 4 and 5. DO you feel the quality is better in 7? In DS9 every single season should be inferior then season 1, Is that a view you share. Same with VOY same with ENT. Hell (though I am not one) there is a lot of people who post about how much they think season 4 of Ent is the show at its best, yet it by far and the lowest ratings, and didn't build as the season went along, do you feel that season is Enterprise at its weakest?
Take TNG's start does anyone here honestly believe that it got the ratings it got simply due to the quality of its show? Or do people believe there might have been pent up demand for new original tv episodes of Trek that help prop up the show, that later shows didn't get because their wasn't a nearly a 20 year gap between new tv episodes of Trek. And that's just one possible example of factors outside of quality that can help or hinder a show.
Of course that's still supposition, I can't speak for the general audience. I can only speak for my personal perception of the quality of stories produced and aired.
Making a statement as fact about why specifically the ratings declined over 13 years, is utterly beyond any information that has ever been released to the public.