I read this at Wiki...
Customers bemoan the loss of engine competition, like Air Lease Corporation's CEO Steven Udvar-Hazy who wants a choice of engines. Airbus points out that handling more than one engine type adds millions of dollars to an airliner cost. Pratt and Whitney said "Engines are no longer commodities...the optimization of the engine and the aircraft becomes more relevant."
OMG!
IMAGINE THE CARBON FOOTPRINT!!!!!..................