https://www.weeklystandard.com/daniel-halper/obama-fires-top-general-without-even-a-phone-call Obama Fires Top General Without Even a Phone Call President Barack Obama fired General James Mattis, the head of Central Command, without even calling the general to let him know he was being replaced. "I am told that General Mattis was travelling and in a meeting when an aide passed him a note telling him that the Pentagon had announced his replacement as head of Central Command. It was news to him -- he hadn't received a phone call or a heads-up from anyone at the Pentagon or the White House," Thomas E. Ricks reports.
Central command is not a high enough post to warrant a president call, it's why he has a "chief of staff". Brb Obama didn't call the janitor for doing a shitty job.
They come and go all the time. For a little comparison, he's been on the job for 700 days and leaves in a bunch more days - under Obama, Panetta served 606 days, Hagel 720 and Ashe Carter 702 (he left when Trump came on) and no one wet their pants over their leaving.