Remember that most of those small stores are able to do this by breaking the terms of service. Accepting MobilePay is NOT free for business, it's not even cheap. As a customers is pretty easy to spot, if the stores MobilePay number is just their phone number, they're breaking the terms of service, and you should pay cash.
I never said it was free, but depending on the service you want, it is significantly cheaper than having a credit card terminal. One of the reasons it’s cheap is because it tells your bank about everything you buy. We worry about social media, but it’s the banks that know what brand of hemorrhoid medicine I purchased last week.
I’m not advocating either solutions, by the way. I’m just pointing out a use case. I mean, I care enough about privacy to not use google or Facebook, and I still use mobile pay because it’s really, really convenient.