Because Adobe hasn't come out with a New version of LR since 2015. There have been numerous point releases, 11 IIRC, but no new actual version upgrade.
OK, let me rephrase the question, is there in the near future an new workable version of LR coming?
I can't surely not be the only professional user that is having problem with extremely slow workflow and constants "not responding" message?
You're not alone with experiencing slowness. Please post your HW/SW specs and your exact CPU type - maybe we can help.
As for the release, Adobe never tells anybody in advance and those who might have an idea are not allowed to tell.