Telefonica and Orange are hardly companies that would just let you lease "valuable" ipv4 addresses without having to pay a hefty sum.

It's not the IP that's the problem.

It's the "anycast" mapping of the IP to geographically and network diverse hosts to connect the user to the "closest" (for some value of latency that stays within the data governance jurisdiction).

To do this, you basically have to own a large enough IP block that backbones will deal with it, and route map it.

https://en.wikipedia.org/wiki/Anycast

They're not random, they're a French non-profit (created by cofounders of nextdns, btw). Why wouldn't people trust them? In my country most people use a DNS hosted by their ISP, and there are a lot of small ISPs all around. I suspect it's similar everywhere. How is it different?

And anyway, I trust a random French small company more than I trust Google.