Good news is, Oracle extended extended extended support for Java 8 will not last forever, and eventually - if you work in a regulated industry - the company WILL have to pull the trigger.
On the other hand, "where there is muck, there is brass", so a little bit of legacy can be beneficial for some.
There's something else amiss here. Compared to other platforms, upgrading Java, even on complex codebases, has never been a nightmare for me.
I upgraded a codebase of approx 100 kloc from Java 7 to Java 8 a couple of years ago. As I didn't want mixed patterns for the same thing throughout the code base I replaced most of the loops with their streaming equivalent. I had the luxury of having the budget for doing so.
Mixing patterns of newer language features alongside older ones can make the code base hard to read.