I too am completely baffled by this, not least because the 2773 was always busy, especially with connecting pax. On the last couple of occasions it has been completely full in both cabins. If it aint broke...
Similarly the re-timing of the 2777 late evening flight into LGW is unhelpful if you are bound for anywhere beyond Central London, particularly if it is late as usual.
Then again, I find BA's whole strategy for JER incomprehensible. The route is presumably a cash cow given the short sector and the healthy loads in both cabins, and yet it remains at LGW with the creaking 737s (and now curiously timed flights). Blue Islands and BE are both now offering decent competition - the LCY flight is usually full, and BE's punctuality knocks BA into a cocked hat. When are BA going to wake up and refine their offering (preferably to LHR or LCY as well)...??