+ Rent, support staff, development costs, regulation and compliance, network, maintenance (cooling, fire suppression + lots more), marketing.

Speaking as someone who did sys admin for a small independent cloud provider, it definitely isn't virtually 100% of operating costs

I'd peg it closer to 75%. There's some significant opex on the endpoint connectivity side as well. That's why a lot of these providers are buying stakes in some of the transoceanic cable projects (and some terrestrial ones as well). Or they're agreeing not to charge each other (kind of sort of- see open bandwidth alliance).

Depreciation is an operating expense. Not a cash expense, but if you ignore depreciation you’ll end up like Detroit.