Change is a leading cause of outages. The cloud providers are constantly changing and upgrading their services, and constantly have downtime ranging from minutes to hours.

In contrast UK gov servers like hmrc.gov.uk (for example) are pretty stable, I can't remember the last time I heard about an outage.

Cloud providers are certainly better at some things (like staying up to date with latest tech), but I'd contend reliability is not one of those things based on their prominent and frequent outages (at least several a year).