Hd25 doesn't look charming either but has already gained much popularity for its sound and portability, although it was meant for the same professional purpose as dt250 and many reviews ABing those two always come to the conclusion dt250 is superior .
Maybe just that beyerdynamic is too famous or infamous for the recessed mids or not fun sounding or neutral represented by dt770/880/990, overshadows the beauty of dt150/dt250 line.
Never heard the DT150 but the DT100 is horrendous for anything that's more than just vocals. Very good for monitoring vocals though.
IMO the D600 and K550 are completely different headphones. The D600 are one of my favourite basshead/fun headphones while the K550 is one of the best closed neutral headphones.