Reading most of the comments, and now adding my two cents.
1) knight rider was one of my top favorites, but david hasselhoffs behavior in recent years has really killed my interest.
2) the simpsons; about halfway through the series, i’d stop watching the episodes halfway through, because it was headed towards sone convoluted situation that homer or bart created, and i just got bored with it. Every episode seemed the same.
3) the arrowverse shows; i got bored with arrow in season 2, when i realized i didn’t really care about any of the characters. With flash, the season long arcs became boring, how many ways can barry screw up? Legends stopped being a dc show, and i couldn’t stand the goofiness. Plus all the good characters left, to be replaced with ones i could care less about. Supergirl was too much social justice. Batwoman became all about a psychotic nutjob. I’m not holding out hope that next season will be any better with it’s emphasis on serial killers. Superman and lois sounds a little too heavy on teen angst and adult drama for my taste.
4) agents of shield; i watched it primarily for coulson, but didn’t care for his entourage. I could never get into the season long arcs, and the spy vs. Spy stuff.
5) doctor who; in a word, steven moffatt. His shows were too drawn out and convoluted; and the companions met some weird fate. Jodie whittakers tenure has been a bit uneven, but with bradley walsh leaving, whatever interest i have in the show is going with him.