The object of the game is usually stated as causing the horse to fall.

Sometimes it is stated as, to see how many the horse can hold up.

My object, and I have never heard this from anyone else, was to get the longest ride possible.

If this is so there is no point in getting the horse to fall, unless there was not enough room for all of the rider to get on.

Then causing the horse to fall means that you all get another ride.