I think you’re exaggerating how much they actually sound like pigs. Closest sound effect to an actual pig noise is
the Do It Gamepseak, and even that clearly isn’t actually a pig – it sounds closer to a sound I’d expect a raptor to make.
A couple of the sound effects sound like they could have been heavily edited from pig squeals, but they certainly aren’t all that piglike any more, and there’s definitely no grunting like in MO going on.