Epic really need to fix the issue of getting engine upgraded for existing games - games start dev at v5.X and years later when they release they don't use current version.
This is very much a non trivial endeavor if the devs deviate to any significant degree from the "off the shelf" engine code.
For example, the Star Wars MMO "The Old Republic" started development on a pre release (<1.0) version of the Hero Engine, and people have constantly asked why the devs don't just port it to the later v2 of Hero Engine.
The response is that the engine variant for SWTOR has been drastically customised and a simple port is not at all a viable move (even as far back as the games initial release).
That being said, Epic have purposefully made it as easy as possible to port between late UE4 and UE5, and likely major versions of UE5 too.
But some dev effort still has to be made, whether small or massive.
I hear about Stalker 2 making a jump from a very early version of UE5 to 5.5, and possibly 5.6 after that.
It stands to reason that if the devs keep non standard stuff to a minimum after the 5.5 upgrade then it will be much easier to make the jump to 5.6 later.