It isn't that severe of a break. Most of the friction was with the libraries with transitive dependencies, like ASM, that depend on a particular bytecode version, using internal classes that were removed (e.g. sun.misc.BASE64Encoder), or the new module system encapsulating APIs that were intended to be internal-only (usually fixable with JVM runtime flags.)

A lot of organizations that use Java are very conservative with their tech changes, and didn't see a compelling reason to upgrade. This was especially true since Android Java still used Java 8, so many popular libraries continued to support Java 8 for their Android userbase.

No. Java 22 will happily execute code built for Java 6.