Another reality was that France had lost all stomach for war after losing 1.7 million men 25 years before in the “war to end all wars”, and Britain couldn’t do much alone (as evidenced between the time of France’s surrender and our entry into the war).
The Brits had the same problem and accounts for a lot of the tactical criticism leveled against Monty. Not to speak to his asshole personality. But Generals will be Generals.