whilsat i agree it's not needed and won't on it's own help, i doubt it will make much difference to the brakes as even with their current size the discs have more than enough heat capacity since they went carbon, it's the pads that usually fail (excluding manufacturing failures)
maybe they're thinking that by going low profile they can achieve a few things, low side walls may allow softer compounds and also reduce rolling resistance and it will force teams to actually use the suspension for the car rather than the tyre sidewalls. one further effect maybe that a lot of the cost to bridgestone is in the construction needed to support the aero loads on such a large sidewalls. it may also be a partiallly marketing sop to whoever supplies the tyres as to joe public the tyres look very old fashioned compared to the modern low profile tyres on road cars despite the opposite being true