Bullsh*t it's to do with Brexit - that's just a convenient excuse. The route is UK-US so really not affected. If they were making money out of it they'd have no problem keeping it going.
Fact is they never charged more than the promo prices - load factors were good but only as they kept prices low.
Brexit will be blamed for plenty of desicsions which are in reality due to a myriad of other reasons.
Still, a shame for Luton and the prospect of long haul from places other than Heathrow and Gatwick.