The only fixes I can think of are log in and install Google Calendar. I tried that, and I also don't get that reminder toggle. I also tried giving Google Maps access to location "all the time" which didn't work either.
There must be some logic in the Google Maps app that determines it not show the toggle for reminders. Since Google apps are closed source we cannot figure out what that reason is. If I were to guess, it's that Google Maps expects either Google Play Services or itself have access to some system permission, and since one or neither of them have system permissions, it just doesn't show the toggle.
Or maybe there is a way to fix it that I haven't thought of and someone else in the GOS community can figure it out!