Physical security and insider threat management for one thing. All big companies tend to hire for these positions from the ranks of law enforcement. Look up lit

Physical security and insider threat management for one thing. All big companies tend to hire for these positions from the ranks of law enforcement. Look up literally any company in the fortune 500 and look at the experience of the chief of security - they don't tend to come with PhDs from Stanford. Moreover Twitter is a target of many government agencies around the world, extremists groups of various shades, and disgruntled randos who believe the Californian elite is stifling their favorite brand of hate. It takes organization and expertise to operate safely within that kind of threat.