Having flown civil airliners (but on the flight deck), I've been aware of this phenomenon for years.

Sadly, it's not that scientific. The cabin crew are usually presented with the meals and quite often will start alternate ends of the aircraft on alternate legs. That doesn't help you if you can't get your choice though.

What do you think they'd rather do? Be able to give everyone their chosen meal, or have to attempt to mollify a disgruntled customer . . .

No-brainer really. Those boys and girls generally just have to suck up the complaint because there's sod all they can do about it.