You have a point about oversubscribing, but you can't really run a VPN service on just any cheap server hosting you can find. That will basically ensure you're on every blocklist under the sun and that defeats the main use most people have for VPNs.
Your can get bare metal servers with unmetered bandwidth from Hetzner for way less then $100 per month. These ips aren't in the ranges that are usually blocked by cloudflare etc.
Those get you two countries, finland and germany. Most VPN countries advertise dozens or up to a hundred countries. Add in OVH who also have unmetered and you also get canada, france, UK and poland. A good start, but I don't think that is what these VPN providers are doing.
Those ranges are also often blocked by sites like netflix, which wouldn't play well with the VPN customers.
