I haven’t found a way to get rid of the extra data, but I did find something that might help it stop growing.
1) Go to your profile (Apple ID) at the top of settings, and then tap iCloud, and then press show all underneath apps using iCloud. In here, find Maps, and disable it from updating and using iCloud. That worked temporarily for me until relatively recently when it spiked again randomly. So, to be safe, you could also do step 2.
2) Go to privacy & security, then go to Location Services, and then go in system services. In here, turn off Routing and Traffic, and I also turned off Significant Locations to be safe.
At least for now, this has prevented the data from growing for me. It initially started growing after deleting the app, so I doubt it’s just “your phone is broken” issue, since there seems to be a common cause for this issue among people. It might not be a widespread issue because many people don’t delete the apps that come with their phones like Maps. I cannot guarantee that this will keep it growing forever, or that it’ll work for everyone, seeing my first solution suddenly stopped working and caused me to seek out the second solution myself. I hope it’ll at least help somebody keep their storage from being clogged by Maps.
Also, resetting and transferring data from a non-corrupted phone that hasn’t deleted Maps didn’t fix it. It seems that as soon as you delete Maps, something goes wrong. Maybe it’s related to iCloud and your Apple ID since my first solution worked temporarily, who knows. But I’ve also seen people claim that as long as you don’t transfer the data directly you’ll be fine? I really have no clue.