Every player has an incentive to lower the price: it attracts customers away from the other players.

They were able to raise their prices all at once because of tariffs. If they'd done that by simply agreeing to raise prices, it would be collusion.

Once the tariffs go away, prices would be naturally expected to fall back to their previous equilibrium because the same forces apply.

It's even more complicated than that, of course. But if there was competition before tariffs then there is competition after tariffs and you'd expect them to act similarly.