You use that account for adsense revenue, but you did not add a secondary recovery email, nor a recovery phone number ?
When you do not have any other recovery, google tries a recovery method based on questions ("when did you register the account", "what's an email address you often contact", ...) where the answer do not need to be strictly exact, have you tried that ? And you failed it ?
If yes to both of those, how do you expect google to differentiate between you and someone else who make the same claims ? Do you want google to give a new password to anyone who makes that claim ("it's my account but i don't remember it's password, nor have its recovery method, nor remember enough to answer questions about it") about your account ?
I believe google's account locking is sometime too hard, and them locking the whole google environnement with it is wrong, but in your case google is doing the right thing in not granting access to someone who cannot in any way prove he should have it.