Belts burn because they sit stationary against a spinning pulley
This happens because the tension is too low so when for instance the blades jamb because of build up under the deck rather than stalling the engine the engine continues to spin and burns the belt .
Usually you can smell & see this because jus like idiots doing burn outs in their cars, it makes a lot of smoke & the burning rubber smell .
Belts shred because they run against some thing that does not rotate so they slide & tear
Usual cause is having them on the wrong side of a belt keeper ( very very very common ) or a frozen bearing in an idler .