Say I want to set up a reminder to pick up some dish soap next time I'm near my neighborhood grocery store. I could open the "Reminders" app and try to do it, but that only works if the store is in my address book for some reason or I know the address. Otherwise I have to search for the grocery store in Safari or Maps, copy the address and paste it into the "address" field for that reminder.
So I've learned my lesson - next time I open the Apple Maps app and search for my neighborhood grocery store, thinking I'll add a reminder from there. But you can't.
Software is super hard, and I get that, and I still love and use geofenced reminders every day. But this particular set of interactions is too complicated for, say, my mom - who just got her first iPhone (and smartphone) - to use, which makes it kind of a problem.