so can they turn off users shops who dont' play anymore?

Out of curiosity, why would they need to/why do you want them to?

I do find it a little annoying to click on a shop with one item, see it sends me back to my shop bc they haven't converted, and debate if I'm going to drop 40m on the only item in SS so my points can languish in someone's Shop Till and not be used, but I don't see why they'd shut down shops of inactive users.

Not all the old legacy shops ARE inactive users though.

Many are active users who don’t have room on the new shops to move their items over yet because of the new limits to how many items can be in a shop so this would be very unfair for them.