Every WiFi network has different speeds. Also, they have the ability to add limitations. So while they may allow one device on the network to access the full speed, they can limit the access of all other devices, or even just one specific device.
Since the speed is fine on your home network, then the only resolution would be to contact who ever is in charge of the other WiFis you are accessing. They may not say the limit the speed and access, but most any modem and/or router can be limited. There is no way around it without the owner of the WiFi network changing it.