Its all to do with the footprint and compound.
For a given weight of car exerting pressure on the ground, the wider the tyre the less pressure the tyre puts to the ground. As a result the tyre doesn't work hard enough to generate heat.
Obviously a softer compound will help.
Look at what the racing Catering vans use as a maximum tyre width!
I went from 225/50/15 to 205?50/15 and could actually feel the tyre temp where as with the wider tyre after a 200mile spirited drive the tyres were no warmer than the air!