El Al are currently very busy in both directions so it’s probably not this. Contrary to appearances in the media, TLV isn’t some sort of war zone that people are fleeing from. My guess is that it’s more that the outbound with the LCA stop is really unappealing (which is not surprising).
I would say the early departure time from LHR and less than daily service is problematic here - if you don't operate daily some of fare comparison sites won't work very well. Accepting that Fridays would be different, I wonder if BA would do better with something like a 10:00 hrs departure from LHR so that some on-carriage traffic could happen, but it's revealing that BA hasn't done that, they are not actively trying to link into early shorthauls and East Coast arrivals. I'm told the route is performing OK in money terms.