Because you're confident that your employer will only use them defensively, and because the system is broken enough that it's genuinely advantageous to good people to have hopelessly vague patents that appear to a judge to cover their inventions.
(That said, my own patent applications probably went to the highest bidder after the sponsoring employer collapsed. So maybe I shouldn't have been so confident they'd remain in good hands.)
The question of future control is why, being involved in patents without some form of contract in place that prevents abuse being in place, bothers me. I maybe trust current management not to be dicks, but trusting all plausible future management not to be dicks is naive.
(That said, my own patent applications probably went to the highest bidder after the sponsoring employer collapsed. So maybe I shouldn't have been so confident they'd remain in good hands.)