At low pressure (<4bar / 60PSI), the tyre beads remains seated against the bead seat. But with higher tyre pressure, the air lifts up the beads and this is where the hooks become mandatory for safety.
At
Mavic, our MTB wheels have turned hookless, but our road wheels are keeping the hook.
...
Those combinations are restrictive, and are valid in respect of the range of pressure recommended on the tyre and on the rim, in order to prevent any blow and consequently inform about safe conditions of use. It is a triple condition: tyre size (width and diameter), rim size (width and diameter) and recommended pressure.