Due to dislike of mechanics: AD&D1, AD&D2, D&D 3, D&D 3.5, T2K 1E, Alma Mater. Bureau 13. ALIENS adventure Game (LEG). Mechwarrior 1e, 3e. Tales from the Floating Vagabond.
Due to Setting: Traveller T4, and TTNE. Aliens Adventure Game. Rifts.
Due to doing it right taking too much planning time: Buffy, Angel, Hero System 4/5/5,5 and Champions 2, 3, 4. Castles & Crusades,
Because my players can't cope with it: Blade Runner, Rolemaster, Spacemaster.
Because there's just too much lore for me to learn: Harn (setting), Talislanta
Because there's too much deep lore for my players: Harn, Talislanta. Renegade Legion Legionnaire, Mechhwarrior 2e,
Because the publisher or author comes across to me as a total schmuck: anything by Mongoose. Anything by Zac Smith or Mandy Morbid. Or, since lockdown, Jim Lot/LotFP.
Lost the bespoke cards: Marvel Super Heroes Adventure Game
Theme issues for the foreseeable future: Paladin: Warriors of Charlemagne, Sorcerer. A whole raft of indie RPGs, most especially Grey Ranks. Tales from the Floating Vagabond. WoD (any)
Special: D&D 5E - combination of so-so mechanics, publisher shenanigans about the OGL, overly corporate, moving towards microtransaction model, just done with it,
Special: MegaTraveller: I have come to realize I no longer enjoy running it enough to make use of it preferable to the thematically similar ALIEN or Coriolis (both Free League), or Star Riders (TFOS post-earth sequel)
Special: Dragonraid: only one objectionable mechanic (quoting scriptures to cast magic), not horrible mechanics. Not its intended audience, either.
Because older editions are so much better: TOR2e, Traveller T4 & T5. WOTC Star Wars, WEG d6 Star Wars 2 revised. Decipher Trek
Because newer editions are so much better: WEG d6 SW 1E & 2 Revised. FASA Trek, Decipher Trek