First, Benny probably isn’t making as much money as Beth, whether by choice or not. Benny did write a book on chess, but the profits from his book are probably negligible. Professional chess-playing is depicted as extremely prestigious in The Queen’s Gambit, but, in reality, it was not a lucrative career (at least in the US, as The Queen’s Gambit also depicts). Benny also seemed less aggressive about seeking out tournaments with cash prizes like Beth.
He doesn’t care about the prestige or money, he just wants to play chess – and he only plays when he wants to play. Likewise, his independent and unsentimental personality indicates that he might not care about owning nicer things and living in a nicer apartment. Then there’s the fact that he lives in New York City, where the cost of living is higher than almost anywhere in the US. But on top of all that, Benny is a gambler.
Like Beth’s struggle with drug and alcohol addiction, Benny has his own vices to cope with his troubles. In The Queen’s Gambit, Beth and Benny play several rounds of speed chess for cash and neither of them is willing to quit until they literally can’t play anymore because they’re out of money. If Benny had a serious gambling problem, it wouldn’t matter how much money he was making as a chess player (which, again, was probably not that much) – the money would be gone, and he would be forced to live in the cheapest apartment he could find.
In the end, neither Benny, Beth, nor any of their friends seemed to mind that Benny didn’t live in a luxury apartment. And despite starting out as rivals, Benny and Beth bond over chess as friends and then, briefly, as lovers. They eventually go their separate ways when Beth sees that Benny is ultimately more singular in his purpose than she realized. Beth does want to travel, fall in love, renovate her home, and buy fashionable clothes. While Beth finds great fulfillment in playing chess, she occasionally uses it as a means to an end throughout The Queen’s Gambit. Beth, at least for part of her life, plays chess to live. Benny, on the other hand, lives to play chess.