How does NextDNS make their Money? And how can they Afford the ipv4 addresses?

I do not distrust the service yet. But for obvious reasons have concerns.

1. I created a new free dns with no account to try, and it randomly generated me 2 ip addresses under 45.90.X.X.
2. I left the page and came back, and it remembered me, so that saves on generating many on refresh. A cookie or something I am sure is responsible for this.
3. I created a new in-private window, didn't even change my public ip address, and I got 2 more ip addresses.
   1. So at this point, I am sitting on 4 addresses with 0 commitments or cost.
      1. I understand that a trial non-account is only good for 7 days and they could then recycle the address, but If I wanted to retain either of them, I would just have to give a burner email.
      2. Furthermore, I could conceivably consume multiple free accounts given I have enough unique email addresses to do so, and then just orient them in order of preference on my devices, so once it stop resolving due to the free limit, it goes on down to the next available service and begins consuming the 300k queries on the next account.

My question then, is how could you afford to do this? Aren't ipv4 addresses limited and a function of your ISP agreements?

ipv6 is virtually unlimited, and the DOH and QUIC protocols don't matter because you can generate unlimited subpages and subdomains for practically free.

But to give free users their own ipv4 addresses makes me very suspicious of this service's cost effectiveness and true source of income.

My thinking, if this is a legitimate service, is that they are merely leasing a port on those ipv4 addresses for use over 53, and that these might be shared ips used somewhere else for some other purpose simultaneously, to make it cheaper?

I don't work in hosting so I wouldn't know