I wouldn't say they don't have enough basses, they play what is given to them IMHO. Zensor just do not make more basses.
But that's what most people want, a little more basses then there is in songs (for example, that's why they master audio CD with more basses, cannot tell you example but there ARE CDs like from 20 years ago and now, the same album, different sound).
for example, headphones - Koss Porta Pro. Good headphones but comparing to Sennheiser PX-100, Portas has more basses, which will hide some details you will hear with PX-100.
And that's why Zensors get a good reviews, they are good, but doesn't mean 5/5 for everyone!