Lots of solutions don't want to - that's fairly different than "can't". I dare say few companies need nigh-100% uptime, and it costs an incredible amount both

Lots of solutions don't want to - that's fairly different than "can't". I dare say few companies need nigh-100% uptime, and it costs an incredible amount both in setup and in maintenance to go from "10s outage while updating" to "no downtime while updating".