One thing I've always loved and respected about Basecamp is how they are not shy about going against herd mentality and do things differently if it works best for them. For example how they don't do daily standups for the sake of it and favour asynchronous communication or how they were a remote company before it became fashionable because of covid.
So if this works for them, I am pretty sure they have done the math and thought about it thoroughly and I completely respect them for it.
Just because something works for many companies, doesn't mean that it works for all companies - so good on them!
I just wonder if they considered smaller cloud providers, GCP and AWS are particularly expensive, but there are smaller tier providers that are much cheaper like Linode, perhaps it wasn't worth the risk for them.