The real problem is they are not as charismatic. They don’t have the life experience to pull from to make a layered character.
most of them were nerds growing up and only was ever into wrestling. And the others were models or something. The excessive drug use and partying is not necessary but these dudes are not in the streets at all so they don’t experience life outside of wrestling.
Meh, a lot of that has more to do with wrestler being able to work 5-7 years before being on TV in a legit program and having a lot of time to develop a character. Guys like Piper or Savage that were incredible in character work from the day 1 were the exception and not the rule.
Another important factor is that in the last 15 years wrestlers put ring work as their main focus and as the main thing that would lead them to gigs and money. We can argue if the ring work nowadays is better or worse than before but that's a different discussion. The main point here is that since the 2000's we've had wrestlers leave character work at the tail end of their priorities so they don't have years of experience working on that stuff so in our view it takes them longer to get a hang of things because we literally see them progress/regress/stay the same every week on TV.
Take Daniel Bryan for example. A prodigy in the ring that was incredible from day one in 2001. It took him 4 years to be a great heel (05-06 in ROH), it took him 12 years to become a great babyface (2013 WWE) and it took him 15 years to become a great promo (2016-17' post retirement).
None of this has anything to do with drug use or backstage behavior