Why did the business tycoons put their support behind William McKinley? Were they they successful

Yes very that's why they threw him out

The business tycoons did throw their entire support fully at William McKinley In order for them to prevent William Jennings Bryan from disrupting and terminating their businesses and destroy their approach, process and activities with his pledge to assist to the fullness the common man and to stand against well established business.

They were successful in their desired choice of vote, as McKinley came out victorious, having victory in the election, as he was vited tbecoming president.