Don't generalize. I, pretty much, am care about it. I wanna know my favourite character's exceptional past if it is exist. And of course Zoro wouldn't care about it, because he DOESN'T KNOW ABOUT IT (yet). And clan pretty much is dead, of course they don't care about him (though O-Toko is still here). If there is a past (like Zoro is a descendant of those Shimotsukis, who left Wano with Kozaburo), i'd like to know, don't know about you.
And thats interesting that you say Zoro doesnt know about it. Why do you say that?
Are you saying Zoro has Amnesia or something that he doesn't know anything that happened to him before he joined that Dojo?
You are making it seem that either Zoro has mysterious past or he has something to hide so that when its revealed Zoro would care or the readers would care.
What if Zoro knows everything about him and it's just that none of it maters to who he is now so the story decided to start at the moment when he met Kuina because she's the most important thing to who Zoro is now.
What if just simply, NONE OF IT MATTER?