I can only assume that WotC heard complaints about that one time that an enemy rolled a bunch of 1s to Save against Stunning Strike and "ruined the campaign" by DMs who don't know jack about encounter design and didn't notice Stunning Strike doing squat the rest of the time. There's a weirdly vocal group of people who think Monk is OP.
Don't forget that crits are actually GOOD in PF2e because they multiply all damage instead of just the base weapon die.