GDPR is what changed this. Before that, registrars had little incentive to hide it for free when they could instead charge you for the service. It was not trivial that Google Domains (rip) came with free privacy proxy right from the beginning.
It not so much that registrars had little incentives, but rather that GDPR defined the concept of legitimate interest as the definition for when registries should give out public information about domain ownership. That allows the contact information to still point to the correct domain owner without going through a proxy, while still creating a small hoop for parties interested to extract ownership information from the registry.
One can see this in practice in that company registration information is usually still available (through often behind a captcha), while personal information of private registrations require additional steps to demonstrate a legitimate interest. All this is also generally occurring at the registry level, rather than at the registrar.
It should be mentioned that privacy proxy is very similar to a straw man registration. If the registered owner is the proxy, then you are trusting that the proxy will honor the contract that is linking you with the property.
So I've walked past Lennart Poettering's house before without knowing it. (And that is not the sort of area where I'd have guessed he would live.)
If I were some kind of crazy maniac, I could pay him a visit and shut down systemd for good. You see why having this information out there is dangerous?
