One additional wrinkle to the tush push is that it WAS illegal until the mid-2000s. Sort of like the 3 point line in basketball, it has taken many years for a team to take advantage of the new rule to its fullest extent.
I think people generally take the perspective of "it used to be illegal, so it's reasonable to make it illegal again" in a way they don't when a team is just doing something new.
It's like when people started to freak out about the "pitch clock" and how it was ruining baseball. The thing is, the pitch clock _always_ existed in the rulebook, it was just never enforced due to lack of technology and just generally never really being a problem.
And then pitchers started taking 1 minute+ to throw a dang pitch and it was ruining the flow of the game. So they started enforcing it.
I think people generally take the perspective of "it used to be illegal, so it's reasonable to make it illegal again" in a way they don't when a team is just doing something new.