"About 50 percent of the Ethernet circuits Windstream buys from XO, or about 32 percent of its Ethernet expense with XO is provisioned as EoC. By using XO's EoC services, Windstream can provide symmetrical bandwidth of up to 100 Mbps to business customers." So XO is a vendor for Windstream for EoC. They want to preserve the supply of EoC, not something that VZ cares about. Verizon is allergic to copper.
Meanwhile Sprint is really pushing its wireline portfolio, something that it had forgotten about for ten years. Sprint's new Ethernet strategy involves two new options -- Ethernet over Copper (EoC) and Ethernet over DOCSIS (EoDOCSIS). Sprint must have struck a deal with Charter and TWC for EoCoax is strictly a MSO offering.
This FCC complaint is just another lever of negotiations. XO used it when Level3 was buying Global Crossing. It happens often.
I'm surprised that either Global Capacity or GTT haven't stepped up to offer WIND and Transbeam EoC services, although maybe the price point isn't as low as XO was offering. Who knows?