It’s atypical motivation but one of the few verticals I know of where the cloud is largely out of the equation.
I think Azure is cheaper for certain workloads as well, and at one point had DCs in places where AWS didn't. But it's mostly the "we already buy X Microsoft product, and they cost about the same, so..."
I’m sure there are some cases where the cost is worth the complexity, but I don’t think it’s cut and dried as written here. Most cloud providers are very reliable, and my guess is that you are more likely to have a self-inflicted outage due to the complexity of your infrastructure than the cloud provider having an outage.
But if I had to make an a priori prediction about which systems would have the better reliability over the long term - cloud-based or those run out of a corporate DC - my money would be on the cloud-based systems.
The cloud providers are going to have better management of power/network/hardware than the most mature government agency, simply because it's a core capability for them.
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).