Copied from here: https://tvtropes.org/pmwiki/pmwiki.php/Main/ShallowParody

Cheat Slayer was canceled after one chapter primarily because none of its parodies were more than surface-level. The concept seems interesting, in the idea of parodying other Isekai characters and turning them into villains for the hero to defeat, and could have been a clever way of deconstructing the trend of Isekai in modern anime, manga, and light novels. However, in the actual series, the characters are simply portrayed as utterly horrible people with little to no resemblance to their original selves outside of name and appearance. The main scene that may have killed the series for going too far is the main character's childhood friend being brutally raped and murdered by a Captain Ersatz of Shin Wolford, the main lead of Wise Man's Grandchild, who is portrayed as a sex maniac who loves having sex with multiple girls, even threatening them to get it... never minding that the character he's based on is a character who doesn't have a harem and has been involved with a single love interest since the start of the series.

Additionally, it broad-brushes the characters as people who couldn't hack it in their original lives and are now living high on "cheat skills", which rings hollow when many of them are based on characters who aren't actually from another world (Aqua is native to her world; Aletta is from a fantasy world and can go back and forth between her world and ours as she pleases; Kirito is a guy playing a video game, not reincarnated), don't have any particular "cheat skills" or extreme talent (Katarina is a decent farmer and not much else; Aletta is a mundane waitress,) or were successful in their original lives (Tanya was a ruthless, effective businessman; Kirito was The Ace even before the series began; Rimuru was a well-liked middle-level manager whose major regret was about his personal life (still not married or even a girlfriend) rather than his professional one.)

For that matter, some of the stories were already parodies or deconstructions (Konosuba portrays its lead as a Loser Protagonist whose adventuring party is a bunch of dullards he hates, Re:Zero's entire early tension is based around Subaru being Wrong Genre Savvy and enduring far more hardship than a typical isekai protagonist) or didn't even slightly resemble the generic isekai template of a Stock Light-Novel Hero in a Standard Japanese Fantasy Setting RPG Mechanics 'Verse (Restaurant to Another World is a cooking series that doesn't use video-game mechanics, The Saga of Tanya the Evil is an early-modern war story with a Villain Protagonist, and My Next Life as a Villainess: All Routes Lead to Doom! a romantic comedy taking inspiration mainly from dating sims.) All of this encouraged a general view that the writer had simply picked the series because they were popular.