Rza explained this. The sample clearance was adding up and once artists caught on the momentum Rza was on, they raised their price tag. These scenarios forced Rza to learn music theory and learn to play piano.
I guess MIA is unaware of Jay's body of work from the late 90's.
Jay's biggest selling album was Vol. 2 Hard Knock Life, selling 5 million copies.
Jay rose to superstardom in '98.