Companies want to signal their unwillingness to tolerate bad behavior from even top employees. There is probably not an epidemic of bad behavior in tech. The number of “brilliant jerk” employees is probably the same as it has been for some time, but post #metoo, Susan Fowler and others, this issue is now more public.
The appearance of intolerance for brilliant jerks is an inexpensive way for companies to signal a type of culture that that is currently popular and desirable, which is why you see them doing it.