They really only started talking about that beef sometime after we all figured out that Dual Wielding has some serious issues with both scaling and not triggering on special attack actions.
So we can assume that Bonus Actions are taking the heat for Dual Wielding being shoehorned into them. And in hindsight, they probably shouldn't have made any Bonus Action Attacks in the first place, but it's far to late for that consideration now. So again, Bonus Actions as a whole are getting dinged for attacking with them.
There is also that blurb about bonus actions not existing until something triggers them, which is an overly complicated explanation for what they intended bonus actions to do (just letting them exist all the time and not be usable until a trigger would have accomplished the same thing). But that has no practical effect on the rule mechanics, just people learning them.
