Why did U.S. Bank buy Union Bank?

Bridge Community Bank 7 Constitution Bank, National Association 4 CUSTOMERS Bank 18 Eagle Rock Bank 4 Farmers & Merchants State Bank 1 First Bank & Trust of Fullerton 1 First Hope Bank, A National Banking Association 4 First National Bank of Clarksdale 4 First National Bank of Waynesboro 3 Homestead Bank 7 Lincoln National Bank of Hodgenville 10 One American Bank 2 Palmetto State Bank 6 PILOT GROVE SVG Bank 7 QNB Bank 29 RIVER VALLEY Community Bank 4 Saint Clair State Bank 3 Waggoner National Bank 3 WOODFOREST National Association National Bank 12 Yoakum National Bank 2