For whatever reason, the key fob range decreases with age. I even changed out the batteries and the range improves a little bit; but, never back like when the vehicle is new.
My guess is the fob is the issue as it ages and get banged around a lot and full of sweat and lint. There is an YouTube videos of a guy doubling the battery in the remote and that 2X the range. The one I saw was for remotes using a single 3v CR2032 and they replace with two thinner 3v CR2016 (for 6v total power).
We use CR1616 and I don't know if there is thinner version we could double up?