My guess is some combination of:

  * Python -> Java jump (e.g. CS1=Python, CS2=Java) is difficult.
  * First real world job in Java in a larger enterprise with lots of older baggage
  * And by a few handful, related to sound technical reasons in their niche area

For me, the jump from Java -> C/C++ in university was hard and I still don't have a good handle on those latter languages. In my first job out of school I was handed a massive C++ library to build an application around with no mentorship and I failed spectacularly. I reacted similarly to the negative Java hate: "Why would anyone use this?"

For me now, as a principal eng, building a greenfield project with Java 17+ now is extremely enjoyable. Interestingly, we've had some HTML/CSS/JS bootcamp devs with no prior coding background succeed in doing Java. And we've had some Python/C university devs struggle. Sample size is too small to be meaningful, I just thought it was interesting.