Got my first bike in 1972, yes I'm older than dirt. For the first few years I would regularly ride with a passenger. I started seeing friends and other riders getting injured from crashes. I started riding solo because I no longer wanted to be responsible if my passenger got injured from a mistake someone or myself made. I don't think I could handle my passenger ending up with life altering injuries. That's just me, but to each their own.
I've had a few requests, "Take my kid for a ride" and I pass on them. No gear no ride and I don't provide. "Oh but just around the block / parking lot." Nope. Same reason.