Considering the 1/4” jack has been around for literal eons (1877, no joke), there’s sort of just tradition when you compare it to the 3.5mm from the 1950s. The primary reason being durability. Your guitar is probably going to be yanked on pretty rough a few times compared to something as little as a phone that will just rip out of your hand. On the guitar, it’d probably damage the port pretty quickly.
Someone watching jam2go???