Dunno where you got that from. It's not for 24h only @RULEZREACHF4N It's back for good (for now).
To answer the question, the chapter was removed in 2021 most probably due to the high license fees. Franchise licenses usually have recurring charges. And after Behaviour (the company behind Dead by Daylight) wasn't willing to pay that much for the next license period, they had to remove it.
I can only imagine that Behaviour and Netflix have come to an agreement - either by willing to pay the price (A LOT of players wanted the Stranger Things chapter to come back), lowering the license fee, changing the selling share, etc. Players (incl. me) can only hope that we also get new content for Stranger Things like skins and/or characters in Dead by Daylight <3