The partnership was officially discontinued around April 2002. KE had multiple notices on its website at least six months before, and continued to accept MR transfers until the end of this summer, which seems rather fair.
I do not know if there were any mailings to this effect however.

While no reasons were given, I suspect MR's conditions are becoming less and less attractive relatively speaking, as many more carriers have left rather than joined the program.

KE is now partnering with DC and offers its own co-branded Visa.