It's very common for bars and restaurants to have a dedicated line for the terminal, but usually they'll skimp on tech (have seen dial-up over POTS or in a fibre-capable premises). Also very common to use 3G or 2.5G.
It'd take a tech all of 5 minutes to diagnose and suggest a fix for 98% of these slow terminals. It's strange seeing businesses not look to fix these issues. If I was a payment provider I'd probably run diagnostics against my customers terminals every day and force poor performing customers to have someone come in and fix it.