The trouble with the <51...Ke5> is that after, say, <52.Rf7...> the Black king will already have lost contact with his own pawns. At the same time, White keeps all its assets intact.

Btw, I am not claiming that 51...Ke5 is any worse than the game. Black is between a rock and hard place: White primary threat is to walk his king to support the Pa7. That can not be stopped by the Black-rook actions alone, lest Pa7 promotes. The Black rook is tied to the a-file and the White king can therefore get through, along the b-file, by harassing that rook if necessary. On the other hand, if Black king tries to help block the White king's progress, then White simply trades Pa7 for the two Black pawns on the K-side and, with two pawns extra, wins. And finally, if Black king marches to forcibly collect the Pa7, then White trades the Pa7 and the two rooks(!). White then easily wins the resulting K+Ps endgame, because Black king would be hopelessly out of play.

Here a just a drafted general defensive plan that I had in mind:

Black can't hinder White's King to support his Pa7 via b-line. It will cost the rook. [but this requires the white rook to block chess from behind] So Black's only chance lies in creating a passer on the kingside, supported by his king to archieve a draw in ♔♖:♔♙ endgame as it could have happend in Alekhine vs Bogoljubov, 1929

There are probably better games with more similarities to this game than in my choosen example.