The only explanation I can think of is that BA do not appreciate the time and effort that people put in to the selection process
Umm, TBH that's pretty unfair on some of the
individuals involved at the BA end. I'd guess the likes of the former recruitment manager (pilot) who used to pop up here and many of those involved in the recruitment process, many of them pilots, really do appreciate the time and effort involved.
However (as always) at a
company level it's all (and I mean everything) governed by the bean counters and I suspect you are right about the level of future applications.