A colleague that works in a tower told me that also Blue Line (BLI) has a "B" on his tail. This could be the reason of why they didn't choose B-Tail as new callsign.
It's full of nice and easy callsign (for example Franky, Ghibli, Relax, Expo, Seagull, Jetset, Stardust and many others) and, considering that for us is not necessary to recognise the company, if the operator has a long or a difficult name or similar to another one it could be easily changed.