All those old books? They still work just fine.
Yeah but that's sortof my point. Sure they work fine, for those that have them. But there are tons of people who have either sold or lost their copies or have copies that are damaged.
I'd love to have a nice and minty fresh collection of 1e books and would even consider a reprint of the basic ruleset. Sure there are people selling them all the time and if you hunt down PDF's you can get pretty much anything, but at the end of the day, people want physical copies that are in good condition and that they don't have to pay through the nose for.
Hell, I bet there's even people who'd just like a reprint of the rules that they could use at the table so that they don't have to use their old copies so that they can keep those in mint condition.