Luckily games that have functions or features that are not present in UE5 or some other publicly accessible engine, still have to add those features to the engine to make use of them. This applies to lots of games and developers. The art of building an engine still is necessary for many developers, even those using UE5 or Unity. So worst case scenario, they have to switch to an inhouse engine development cycle and spend that much more time and money building an engine that makes them nothing in return on the hope that the engine they make, will save them substantial development the across future titles.