- Total dependency on an engine's build system
- Lack of official support for uncommon platforms
- Extremely low expected ROI even if it were possible to deliver on other platforms
Gamedevs aren't in the business of building platforms, they're in the business (mostly) of consuming them and going where the players are.
Gamedevs not updating is because
- The engines themselves are indeed outrageously brittle at times, with LTS releases sometimes containing significant bugs that persist against newer releases of minor and major versions
- New releases can actually cause dramatic regressions, not just in terms of bugs, but in terms of features, stability, binary size, and more
- AAAs are wasting time chasing the next big thing, non-AAAs are struggling with few people and need to constantly be building the next thing because they're building products, not services
- Gamedevs are largely media/entertainment companies, very few act like technology companies