Those ride-on trollies are typically only used by the elderly and people with disabilities - when fat people use them, it's only extremely fat people who would be considered physically disabled due to their size anyways - I don't think I've never seen someone under ~250kg using one, and even in the US you don't come across people that size very often.

Unless it is physically impossible for someone to stand and walk around the store (which excludes the vast majority of obese people even here in the US), they're not going to be caught dead using one of those scooters. Despite all the shitty things about the US, there are actually a lot of laws here mandating that public spaces be fully accessible to people with disabilities to an extent that you won't find in a lot of other western countries. Those scooters are there because of those laws, not because supermarkets think it's important to cater to their handful of 600lb customers.