Some people just enjoy bad sending. If you don't believe it just listen around for a few days on the CW segments.
Some people believe it gives them "character" of personal "flavor". Some describe it as "playing music" and therefore open to their personal interpretation of that "music". You would never tell a musician that his playing was incorrect, as music is open for interpretation.
I have always considered it just bad sending, and making copy more difficult on the other end.
As an example I often hear dah di dah dit dit dah di dah . sent and meant to be a CQ. Over and over again with the Q murdered as a dit dah di dah. Why they do this I don't know, but an awful lot of guy send CQ in this manner. Lots of other examples, including MANY examples of poor bug sending.