So what is stopping someone from holding a gun to your head and forcing you to conduct a wire transfer over the phone or internet?

Online banking wire transfers are subject to a relatively low daily limit. You must appear in person and show ID to wire large amounts of money.

The victim may also have a chance to cancel the transfer, because they’re not instant. (especially outside of business hours)

It’s just not an attractive way to mug someone, it’s easier to take them to an ATM.