This would compromise on security (for this scheme, time window will presumably be longer, many more keys that can be compromised) and would create an explosion

This would compromise on security (for this scheme, time window will presumably be longer, many more keys that can be compromised) and would create an explosion of keys for the user to manage, effectively offloading that work to your customers. I don't know that it would present a simpler experience to force your customers to have a different key for every service for every region. Anyway, this is from the perspective of a large service provider. For side projects or smaller services, yeah simple can be good. But it really depends on your security requirements, threat model, customer requirements, etc.