To the point that if someone would take the hard work to try fork and implement the features some consider missing, they would be burned on the fire instead of praised for their work, which is why anyone with the skills of doing it just goes elsewhere instead.

Do you think really Java or any other professional language would accept some language feature which was developed prior to explicit approval from committers?

If someone thinks since they have developed feature and put lot of hardwork in it so language maintainers have to merge it. I am sure they would have no option but to invent their own language.

Yes, that is how a large majority of contributions work.

Language improvement proposals aren't taken in just with words on paper.