Have you ever actually visited someone in prison? I have and I'd say meeting up in a coffee shop is infinitely preferable. You can only go there during a specific time. You have to go through a long screening process that might involve taking off undergarments for inspection so you have to get there early. You awkwardly sit in a room with the inmate at a table being constantly watched. You only get a small amount of time with them. It's not really very "social."
Prisons allow visitors because prisoners generally can't leave. It's a much better deal IMO to be able to leave but not have visitors come to you.