[StilesCrisis]

The flagships are the laggards usually! They are large, complex projects with lots of ongoing maintenance and commitments. "Upgrading to the new compiler" is seen as tech debt payback... there are deadlines, new features, and more important things to implement!

[locknitpicker]

Upgrading a compiler in production code is always a major task. It often involves introducing breaking changes in dependencies, some of which are far from trivial to fix.

If you tell a Product Manager that you want to upgrade a compiler just because, and all it will take is a month or two of work including full regression tests on all target platforms and collaboration from all teams, that isn't an easy sell.