score:13
First, review the reasons for the French Revolution - pre-eminent among those reasons is that the French state was bankrupt. It could not pay bills or collect taxes. This was not a temporary problem, but a structural problem. See Revolutions Podcast (I linked to one episode, but strongly recommend the rest) is an excellent source. The French government was dysfunctional from the absolutist head, through the corrupt middle down to the ineffective and disengaged bottom.
Two further complexities:
1) If you can't pay your army, it isn't your army. If the King can't pay his bills, he doesn't have an army, he has a bunch of armed people with a grudge.
2) Due to peculiarities of the French system, most of the army did not report directly to the King, but to the high nobility. Duncan covers this better than I can.
Postscript - my professional historian girlfriend pointed out that our modern notions of nationalism are the result of the French Revolution. In the ancien regime, soldier's weren't fighting for "France!", they were fighting for pay, for their unit, for their leadership, but "France" was an abstraction. Soldiering was also a substantially lower status profession at the time.
Upvote:4
One reason is that the French "Army" (its officers actually) looked up to a former general named the Marquis de Lafayette. He was a war hero who had fought for the Americans in the American Revolution, helping to defeat England, (France's arch enemy), and was firmly on the side of French Revolutionaries.
Lafayette was a mediator that was trusted by both sides. At one point, he calmed revolutionary tensions by kissing the hand of Queen Marie Antoinette in public.