This story was at once fascinating and repelling to me. The guy clearly got away with what he could, because he could... his previous lies led to success, so he continued to manipulate and lie. As to why chose to lie, and leave obvious clues that he's lying (the fascination with Mr. Ripley, the Munchausen's PhD that never was) well, he enjoyed lying. He enjoyed putting one over the clueless masses. I won't say he's a psychopath, but his behavior certainly is. He had all the advantages in the world, yet chose to take the extra step(s) that let him pull ahead a little further.
It also seems he thought no one recognized him for what he was. I think a lot of people were suspicious. From the article in New Yorker friends and colleagues did, they just didn't know what to do about it. How do you walk up to a co-worker and say "You're a complete and utter liar?" There is no good way. How do you tell his superior that? "So-and-so's brother is actually alive. Here's his address in New York." What would the boss think of you? What would the boss do about him? Adults should not have to be accused of blatantly lying like toddlers and assuming other adults are stupid enough to believe their lies. (Sounds like a certain president, no?)
And the thing is, it's so easy even for average people to dig up what's true what isn't. Calls to a university, address traces, social media connections. It can take a few days, working full time, but it can be done.
I don't believe this guy for a minute that BPD is to blame for his shenanigans. It's another lie.