Colos will rarely lose power, but having your line cut due to a backhoe is pretty common. Even in top tier facilities I observed some loss of service every 6-12 months, add in some misconfiguration risk and Colo failure becomes a frighteningly common affair.

This can be mitigated through redundant service providers, careful checks on shared interconnects and other measures - but having "hard" failure isolation at the facility level will also get you there with less chance of someone doing something dumb.