I recently (2020) played BG1 and 2 with their expansions and on the one hand you're right... But on the other getting the same story with 10x the graphics and some modern QoL would be great. Reaching BG3's massive audience - that isn't all 90s nostalgia gamers - with a story that's new-to-them would really help cement it in the same way BG2 did for BG1.
They are, but, even as someone who really enjoyed playing them without any nostalgia for them, I would have liked them all the more with a better combat system that is properly turn based and three-dimensional as the one in BG3 is.
I know for a fact that there is a sizeable portion of players that don't think that BG3 is strictly or at all better, but at the same time, a lot of people can't get into BG1 because they really don't enjoy its combat.
I'd absolutely adore a mod that gives us the BG1 story in BG3 and I think it would really boost accessibility. It would also be an enormous amount of effort to represent it well, especially in a way that tries to capture it in a recognizable form.