Because they can, it will make their product more competitive and because it said so on one of the rumor websites (forgot which one).
Still not sure of course but according to the Macrumors buying guide it makes sense.
Recommendation Buy only if you need it - Approaching the end of a cycle
Last Release February 24, 2011
Days Since Update 151 (Avg = 215)
https://buyersguide.macrumors.com//#MacBook_Pro