After 3.Rxd8 Rxd8 4.Rxd8 Kxd8! White doesn't achieve c4-c5 either, just like in the main line.

Preparing ...Qe7 with some pressure on the b4-pawn. Black has no problems.

A first step to a future ...f5-f4, undermining the white pawn chain.

5.axb5? f3 Black obtains a strong attack.

Black isn't interested in a draw by repetition and directs his last piece at the enemy kingside.

With a strong initiative.

Preparing b5-b6 with decisive damage to Black's pawn chain.

Or 2...dxc5 3.Qxe5 with a crushing advantage.

3...cxb6 4.cxd6 Qf8 5.Qxb6 is equally hopeless.