During the early 20th century, it was possible to observe the colossal effect nationalism had on the peoples of Ottoman Empire to a great degree(like the other imperial powers at the time), and Arabs just weren't an exception. Knowing that, the British manipulated and supplied the Arab unrest to pin down the Ottoman troops around Hejaz, so that they wouldn't have to worry about Turkish reinforcements assaulting Suez Canal. Needles to say, it worked. Cut off from their only supply line, the Ottoman forces were unable to go on a major offensive.

For your second question; Turkish forces managed to hold a lot of land, including Medina, until 1919. And by that time, the borders were already being drawn as local Arab leaders struggled for power; the very guy who started the rebellion for example, Sherif Hussein, declared himself the King of Hejaz and did not really care about the Arabs outside his domain.

Arab leaders who didn't agree with France and Britain dividing the land as they saw fit couldn't oppose them effectively. Some were left too weak without British support, and some were busy fighting each other over both land and titles(Hussein had declared himself Caliph). In short, it was an uneven match.