Airlines cannot try to put systems in place to deal with the issues? This isn't just about individuals but also organisations. You have to believe that organisations would also want to hide things even if mandated and incentivised otherwise.
So getting pilots to self report has been very unsuccessful because of how badly it ends for them.
A couple of days ago the senate had to pass a bill to make mental health medication access easier for pilots. We will see if it helps, but it doesn't solve the root cause (punitive measures) so I doubt it'll move the needle.
I do agree with you that a proper regulatory framework with clearly defined obligations is better than one off overly-punitive fines and arrests.