As
@lazyboy97o said, it's cheaper to just put some switchbacks outside. And to be fair, outdoor queues have been quite common across the parks, going right back to the early days of Disneyland. At least this Ratatouille one is properly covered from the start, unlike SDD where they stupidly didn't include proper shade structures for much of the queue in the original build and had to retrofit them in.
Sometimes I wonder how much of this comes from WDI being based in Glendale. It's one thing to stand outside in SoCal during the summer; it's quite another to do it in Central Florida (CenFla?), and I can't help but think some Imagineers forget or ignore that fact. I know there are some field offices at WDW, but I don't know how much say those offices have in attraction design.