When you set up a hot-spot,
- Wi-Fi is like a driveway in front of your house.
- Cellular data is like a city street in front of your house.
- The Internet is like the massive network of roads that spans the whole continent.
- Your iPhone is like the connection between the end of your driveway, and the city streets.
- Devices that might use a hotspot are like cars parked in the driveway or garage of your house.
If you could set up a Wi-Fi hotspot when cellular data was turned off, it would be pretty useless. Other devices that connected to your phone via Wi-Fi could talk to your phone, and maybe to each other, but none of them would have the ability to get to the Internet.
Since people who are looking for hotspots are generally looking for the ability to get to the Internet … not merely the ability to turn around in the driveway … the idea of using a Wi-Fi hot-spot on an iPhone when cellular data is turned off does not make much sense.