Been reading the reviews and such, CS Source was experimental and just not the same feel as CS 1.6, CS GO does have the feel although not everybody is convinced though. Me? GO is convinced for me, Source just doesn't have the same gameplay.
Without any prior knowledge as to the reasoning behind that, my assumption is that they probably did that so every server wouldn't be covered in porn sprays. If so, good idea on their part, however, spraying was the "t-bagging" of CS, so it's kind of a shame to hear about it.