The counterpoint to this is many studios are sequel factories, or producing games that are at least broadly in the same genre continuously, and each game starts as a fork of the last, which is how you end up with things like the COD engine or Source 2 having a direct lineage to engines from 90s quake games. So "Assassins Creed: Odyssey" may not be an ongoing service, but "Assassins Creed" is, and tech carries forward from one to the next.