It's been this way for the longest time, if not from the very beginning. Note that EQM only on the LGW-DXB that's CO codeshare.

For LGW-DXB, only EK12 and EK16. Not EK10.

For DXB-LGW, only EK11. Not EK15, not EK9

Basically, only those with direction connections on CO to/from the US.