That's odd. Most airlines allow BT in airplane mode. Every one I've flown in the last 5 years at least, and that includes to Europe. Now, having said that, I have not flown a local/regional into Scotland...I have wired earbuds because you're not supposed to use Bluetooth stuff on the local aeroplanes here (lots of folk do anyway but I feel like ignoring supposed "safety" rules is a bad idea unless you actually know something about the topic in question). I've never paid quite as much as $50 but the wires always seem to get damaged really quickly if you're using them out & about and putting them in you bag or a pocket. Wireless last much longer ime.
so we're guessing it's an old rule that they just never got round to removing from the safety briefing.