If I recall correctly at the time, all personnel was moved out of the base and advanced "warning" of the strike was given by Iran. It seems like it was a calculated way for them to save face negotiated between the US and Iran, rather than ratchet up the possibility of war at the time. Trump did not want war with Iran.

Now all bets are off the table. Whomever it is talking into Biden's earpiece wants and will get war back on the menu.