The problem is that anything but thermal is expensive. Not in the paper (thermal paper is obviously more expensive than plain), but in total cost.

If it's got an ink cartridge or a ribbon, then that's a second consumable (ink+paper probably equals out to thermal paper). The more important problem is that when you have a second consumable, you have two different things that the operator has to deal with, probably at different times. Now, instead of just swapping out a roll of paper, the cashier will also have to swap out a ribbon.

That's an extra step, at probably a different time (ribbons/ink carts and paper are unlikely to run out at the same moment). It's one more thing to go wrong (either the ink cart can clog or the ribbon can twist up), and overall it's more of a maintenance hassle. When you run a high-volume operation, this hassle is not worth it.

It's easy to argue that thermals aren't as good, but unless you account for the whole chain that caused them to choose the thermal, you aren't going to make any progress in understanding or changing anything.

The only way they'll switch out is if they think it's in their best interest. Complain to them. Loudly.