If for some reason the OFDM ack isn't gotten, then neither side can understand the timings to actually communicate. So you end up with non-pairing hell. This especially happens between different "specs" of BT.
2. Raises noise floor for whole BT carveout
If they had 2 control channels, and then moved the comms to an agreed upon channel, this would never be an issue. Look at how Simplex ham radio works - do announce on a channel, and move elsewhere when agreed upon. But whatever you do, don't just blanket the whole channel (or all of 2m) for 'reasons'. And heavier bandwidth BT can take over multiple channels. This isn't easy, but nowhere near as difficult/stupid as what it is now.
3. Multiple incompatible BT specs
BT used to be a IEEE spec. Not any more. And there's more than 7 or so major versions. Oh, and many are incompatible with each other. What's that XKCD about "Standards"? :(
4. arcane pairing sequences
Again, pairing is crazy complex. I'll have to post the actual IQ data and show a comparison between FM (88MHz-108MHz), 2m amateur radio (144MHz-148MHz), analog TV, 802.11BGN wifi, and what BT looks like in various states.
To sum it up, "They're doing it wrong".
Fragile OFDM? Any other rock solid narrowband interference mitigation techniques that are not electronically complex?
No dedicated control channel? Remember, BT just like wifi implies operation along non-cooperative 3rd parties.
While bandwidth for Bluetooth is not great, it'll work for small amount of information exchange and at the very least discovery of other methods for communication like ad-hoc wifi.
I'd be happy to hear about more details why Bluetooth is crummy as well.