Crazy? No, certainly not. Until very recently, it was unusual, but not crazy.
I put up a thread on MN a while ago titled "I don't do relationships". The quote referred to a young woman I met at a party who used exactly those words. Several people on the thread described friends and family who feel this way. One woman said two of her teenage children were dead against relationships, and that many of their friends also seemed uninterested. The young are far more cynical and wary (possibly because they go online and read endless horror stories about miserable, toxic, controlling, hellish partners – something they used to have to discover for themselves).
I suspect it will become more and more common – like being gay, or having an open relationship, or being polyamorous, or whatever. Society is more tolerant now. And so people who used to hide away, or force themselves to live in ways they didn't like, can now relax. Long-term relationship don't suit everybody. Some people have high sex drives, some low. Some people crave intimacy, and can't bear to be alone, others find intimacy suffocating and crave solitude.
Until very recently, society was brutal. Unless you were married young (to a member of the opposite sex), had kids and stayed with the father, you were an oddity. Nobody wants to be outside the tribe. We're hard-wired to crave acceptence. And so many people endured hellish relationships because, well, that was what you did. Both my sets of grandparents were in nightmare marriages, and both stuck them out to the bitter end. THAT was crazy. Both my paternal grandfather, and my maternal grandmother, would have been much happier if they'd never married. My grandfather was a kind, easy-going chap who liked his beer and darts. He married late, to a screeching, selfish monster, and had three children he didn't really want. His life was a total misery. He was a born bachelor, and should have stayed like that. If he were born today, I'm sure he wouldn't bother.
Actually, when you think about it, we didn't evolve to live in a small brick box with a stranger for 60 years, sharing a toilet, sleeping with them, eating with them, watching TV with them, going on holiday with them, year in and year out for decade and after decade, never having sex with anyone else, etc.