Comment by dcminter

Some of the weirder choices have been the result of a desire to avoid making breaking changes to JVM bytecode.

Also there was a long period when changes were very lumpy - it could be multiple years for a feature to make it into the release, and anything that might screw up other features got a lot of pushback. Then other conventions/tools emerged that reduced the urgency (e.g. the Lombok stuff)

Edit: I should add that it's now on a fixed 6-monthly release cycle which IMO works much better.