Random, or any kind of large-scale layoffs make everyone in the company each other's enemy. It destroys cooperation to the point that most people actively start trying to sabotage each other (because climbing the ladder is no longer the primary concern: you must make sure there's people above you on the firing list)

You should fix overhiring by firing the people that overhired. That never happens though because there's no accountability in leadership in any major tech company.