so, because somethings popular,its not worth discussing.
well the point is this, the c# d is better for playing the right chords in D major,
the GD is better for playing all the correct chords in D major and Gmajor and Eminor.and some tunes in a mixolydian.
The BC is fully chromatic on the right hand side,but in certain keys,the bass chords,are not there to fit with the right hand or the players play the wrong bass chords.
a classic example are players in [a minor ]using a major chords,when the tune is in a minor[Bizarre].
the two and half row gd box allows the player to play in a major.
   there are,many very good bc box players some use their right hand only,some like Bobby Gardiner,know when to use their basses and when not.
I have yet to hear c#d players playing wrong bass chords in d major.
yet d major like a minor seems to be more problematical when it comes to playing bass chords for BC Players,.
The DG is the best box for playing irish music in the key of D and G,and having all the correct basses easily available,[if thatshow youwish to play]but obviously is no good for A major.
the two and a half row dg.,only partly solves this problem.