Not sure why EIN was chosen, but looking from outside in, is there a potential link between Phillips HQ in EIN and South London?
This might be a factor in the choice for this route but not entirely sure.
On another side, there are still gaps in the UK regions where EI could make "hay". Examples would be potential non FR base airports.
Excluding LHR, there are at least 5 airports with over 2 million pax where FR does not yet have a base.