How do all these proxy for rent services have thousands of IPv4 addresses?

I came across these services that promise tens of thousands of IP addresses for a monthly subscription. Ex. Stormproxies, Blazingseollc...

From what I understand, these services use a reverse proxy to route you through, and each router gets only one IPv4 address.

So how do they have tens of thousands of IPv4 addresses to rotate their users between?

Are they just renting servers from a bunch of different providers, like AWS, and routing their customers through these servers?