Apple seems weird about that and I'm not sure why, maybe accuracy or creepiness factor?
A feature I would love is to toggle "answer calls on speakerphone" based on location, so that I can answer a call with my phone on the desk while I'm at home and not have my ear blasted off taking a call when I'm walking down the street.
I can set location-based alerts manually. For me, or for those who voluntarily already share their location with me. No reason Siri can’t drive those same notifications.
Edit: to be clear, Siri doesn’t. Still no reason it shouldn’t be able to.
Apple Reminders has a feature to remind you when you are leaving or arriving at a location. It's super useful! But it's not super low friction to add to a Reminder via UI (it's buried at the bottom of the edit screen), so it's a feature ideally suited for a voice-based reminder. Nevertheless, nobody implemented it.