While the time from child to mid twenties is definitely the parent's fault, after that point you can try every trick in the book it won't achieve a thing. Once someone masters weaponized incompetence they basically need a life or death wake-up call to do anything about it, and even then they might still not learn anything.

No one's literally impossible to reform, but many people cross a point that requires a practically impossible amount of investment to reform.

It's bad parenting alright. But I don't believe that they've never made an effort before. More likely the guy has resisted any attempt to get him to be independent.