Dameion

If you have to blame any IP... Blame Attack on Titan... They strung their fans with "FINAL ----" across years, only to make another "FINAL ----" again. Literal memes about if the final season was going to be the final season.

Not saying the show was bad at all, just saying their Marketing carried that IP and its fans so hard across years of anticipation just to bait and add another season.

Demon Slayer isnt any different besides how well the animation quality in this was executed. Anime has always had both movies and series of popular IPs, so this isnt anything new. It just seems like so because it's mainstream popular, compared fans having to accept their favorite show may or may not come out with more content, and if it does, the fans are hype, if it doesnt, the fans will still go rewatch what they already loved... Same reason why so many productions, movies, games, shows; have so many remakes/remastered and sequels.