>> These experiences of power outages is weird to me. What I consider "typical" data center design should make it really hard to lose power.

At least 30% of datacenter outages that we had with a large company were due to some power related issues.

Just a simple small scale one: the technician accidentally plugged in the redundant circuits into the same source power link. When we lost a phase it took down the 2/3 of the capacity instead of 1/3. Hoops.