> Didn't companies historically own their own compute?

Historically, companies got their compute needs supplied by mainframe vendors like IBM and others. The gear might have sat on premises in a computer room/data center, but they didn't really own it in any real sense.

> Basically I don't understand what they're selling if it's not what people already call clusters.

Is it really a cluster when the whole machine is an integrated rack and workloads are automatically migrated within the rack so that any impending failure doesn't disrupt operation? That's a lot closer to a single node.