They usually don’t say they are building their own datacenter, though. It is different to say something like, “our website runs in our datacenter” than saying you built a datacenter. You would still say, “at our office buildings”, even if you are only renting a few offices in an office park.
We built an office building would be the analogy.
Don't the hyperscalers outsource datacenter construction and operation? Maybe it's not clear where to draw the line because the datacenters are owned or operated by disposable shell companies for various reasons.
When you rent an apartment, you can still invite people to your apartment for drinks. But you don't claim to have built an apartment.