Where to get competent staff?
Since I'm interviewing candidates very regularly for a variety of different infosec roles as a part of my job, I've found that one reason for burnout is the difficulty in finding competent staff. My employer has no incentive to fail to find good candidates, but so few of the candidates sent my way am I able to give a thumbs up for more than a tier-1 secops team staff -- the kind that does nothing but pre-written instructions developed by someone else.
I've seen roles go unfilled for a year or longer just trying to find a competent low to mid level security analyst. Add in any middle to high level skill and expect more of a senior technical security role, and the time can increase even more.
Easier to burn out when people leave and are not replaced, not because management won't let them be replaced, but because no one can find anyone they feel has the skills to be worth the cost of the chair they sit in.