The biggest reason the old M-14s were pulled out of cold storage was because we needed something with better long range performance than the M-16/M-4, and the M-14s were available, without having to go through any kind of new procurement program, and at minimal cost (especially the first ones to be pulled out, which got a scope and hopefully a cheek riser of some sort. The Sage EBR stock came later). (Without the Hughes Amendment, I wonder if all those M-14s would have been sold through the CMP?)
The Army and Marines did buy an AR-10 variant - the Knights Armament SR-25, aka Mk 11 Mod 0 aka M110 SASS, as a partial replacement for both the M24 and M40A1 bolt action sniper rifles, as well as to try to fill the SDMR role that the M-14 EBR was doing stopgap duty as.
The M110 is, as of 2018, being replaced by a slightly more distant AR-10 derivative, the M110A1, which is based on the HK G28, which derives from the HK 417.