[Someone1234]

They could run fine on the CPU too. But these are mobile devices, therefore battery usage is another significant metric. Dedicated hardware is more energy efficient than general hardware, and GPU in particular is a power-hog.

[vel0city]

Exactly. It's the same thing as video or audio encoding and decoding. Sure the CPU could do it, potentially use the GPU, but having actual hardware encoders and decoders for the most common codecs will save a lot of energy.