maybe the goal is instead to try to get ahead of regulation by implementing a system that is easily bypassed by most kids (like these video based age estimations). Then they can show this to the regulator and be like: “look were already doing everything we can, no need to actually put the regulation in place”.

You can disable showing adult games from the store in the store preferences.

https://store.steampowered.com/account/preferences

This setting is apparently disabled by default, so at some point you enabled it.