The politics of firing cabinet secretaries

In the aftermath of the revelation of Trump's henchmen having a chat using the Signal app, 

a number of Democrats are demanding that Secretary of Defense Peter Hegseth be fired.

Where were those Democrats when Hegseth's predecessor Lloyd Austin popped off into a hospital for a prostate operation, without telling his supervisors where he was because 

it would be too embarrassing?

So Austin can make a mistake, 

but when Hegseth possibly makes a mistake (the record is somewhat ambiguous on that), 

that is a firing offense?