That happened because the concrete curb was wider than the wall at those points, or because the whole curb was slightly oversized and whoever built the garage didn't want to make a 1/2" adjustment to make the outside walls sit flush with the exterior curb. I bet where the wall is flush on the inside of the garage either attaches to the house or has some funky siding issues outside.

That's something you needed to address before insulating/drywalling - as it is all you can really do is scribe out some filler and put that in behind the baseboard. It will look weird.

Consider some built-ins for that wall instead. Cabinets, etc, will hide that.