I approach every medium with certain expectations set by the story and if the story reaches those expectation then that counts for something , but if it misses those expectations wildly then that makes an impact. Because Bleach set the bar high for itself when it failed to meet those expectations it gets judged harsher.
It doesn't have to be anything special but it fails miserably at being a sequential story in visual medium. There is no auteur-ship behind FT. It's just a random mix of popular shonen elements executed in the worst way without any reason or rhythm, to the point where it would make a 8 year old kid blush from embarrassment. Even Bleach, despite it's pretentious moments, has Kubo written all over it. You can't say the same for FT because it doesn't have a self-identity or the author's touch behind it.
Because Fairy Tail never strived to be better than "ok" when it does slightly worse or better I'm not going to say it's awful or great. It's just basically the same. FT is just same ol' FT whereas Bleach is a roller coaster right that doesn't end as is plummets down the slope and you can't help but get thrilled once in a while.
Neither did Twilight or thousands of other shitty works. Sorry but readers shouldn't have to lower their expectations of basic storytelling just because the series doesn't "strived" to be more than a shitty shonen series.
Few people are going to look at Fairy Tail and think 'how great it used to be' or how 'bad its gotten' because the changes in quality do not warrant those responses.
Because people like to ignore FT's massive massive problems when it has some of the most basic and amateurish writing mistakes.