That's the spec on e-bikes for the foreseeable.
Gonna guess its just because that's all that is available for omnium to use, hardly any 11 or 12s shifters or mechs or cassettes available in upcoming supply. Nexus 5 does not suit the typical omnium user for sure.
@BrickMan started
London Fixed Gear and Single-Speed is a community of fixed gear and single-speed cyclists.
That's the spec on e-bikes for the foreseeable.