You and 10 other people are connected to a public hot-spot.

In public WLAN environments, security and privacy are paramount. To prevent clients from communicating directly with each other, many WLANs implement peer-to-peer blocking (also known as client isolation). This feature ensures that each client can communicate with the internet but not with other clients on the same network, thereby enhancing security.

The CWDP-305 Official Study and Reference Guide discusses this feature:

"Client isolation prevents wireless clients from communicating directly with each other, which is especially important in public or guest networks to protect user privacy and security."

Therefore, the inability to detect other devices on the subnet is likely due to peer-to-peer blocking being enabled on the WLAN infrastructure.