My late MIL was a sparkling conversationalist and always showed an interest in other people. Sometimes she talked about things that had happened 50 years ago, but it was always some juicy scandal that she remembered from years ago, and always about at least the family of people I did know. I envied her memory, to be honest! And although she did gossip, she was never malicious, just mischievous.
My grandmother only had one topic of conversation, ever. India. She left India when she was 19, but in her head she always lived there (she wasn't Indian, btw, she had first moved there when she was about 8). As a child, I was fascinated by her stories about her life there, but by the time I was 16 I was ready to scream at her! (We spent every 3rd and 9th weekend together and some half terms). It wasn't really the stories that drove me mad, it was the total self-obsession of talking at everyone who came close enough about this one thing, over and over again. There was no conversation involved, just her talking at people. And I'd have rather not heard about her miscarriage, her health problems and her sex life- she really did overshare, and if it happened in India then I heard about it repeatedly.
OP, I wonder if your parents seem worse to you than to your partner. Mine often used to make me cringe, and the only allowed topic of conversation at their table is How Wonderful My Sister Is. Nobody else seems really bothered though, except in a vague, eye-rolling way. They don't talk to me at all now and I certainly won't miss them when they are dead, but I do appreciate that most parents aren't violent abusers and deserve much gentler treatment.
The only time I've been really irritated by a person who does this was when I was certain it was being done deliberately to exclude me. She was elderly (a cousin of my husband's) but according to Mr Carpet, she has always been a cow and her age has nothing to do with it.
In your case, OP, I'd let it go. Many years in the future, you will probably remember it as a charming quirk, and if they are otherwise nice and you love them, I wouldn't want to risk upsetting them. Some people just don't like to leave a silence and feel obliged to say almost anything to fill it.