That’s because the Marines are going more seamobile and focusing on fighting in the Pacific in future, and the M1 has gotten so heavy that even the largest landing craft we have, the LCAC, can only carry one to the beach per trip. Pretty bad.
The M-1 has become a mega beast. I was looking one over at the local truck stop the other day. All kinds of bolt on reactive armor and defensive items. there is currently a regular flow of them in my part of the world. Headed for some rework project at the nearby depot.