Why is this unreasonable?
I can see that it would be troublesome if the hotel tried to interfere with the connection between your device and your mobile/cellular provider.
Preventing guests from setting up Wi-Fi Access Points (personal Hot-Spots) on your premises seems reasonable.
There are only 11 Wi-Fi channels in the 2.4 GHz band and you can't run more than 3 of them in the same area - they will interfere. (I'm skipping over the 5GHZ band and channel-bonding to keep it simple).
Having guests put up Wi-Fi hot-spots of their own will interfere with the hotel's ability to provide (free or paid) Wi-Fi on their premises.
Or am I missing the point? Are the personal Wi-Fi hotspots so low-power that each hotel room could run it's own without interfering with those in the other rooms - or with a hotel provided Wi-Fi service?