The British reneged on them.
The British are Arabists.
actually, the British did a lot of stuff that was Hinkey, whether it was going back on their agreements with the Arabs to fight the Ottomans for them, (only to give the land to the Zionists) or trying to take the Suez Canal from Egypt and conspiring with the Zionists to do so.
You see, how the Arab world sees Zionism? White European Colonialism by other means.