No surprise many people dont know him, he never had some major success on international tournaments (at least in singles) until now. He is a decent doubles-player and was European Champion in Mixed Doubles many times but i can't rememver him being somewhere near the medal places on any major tournament in the last years.
As someone said before he is not the stereotype athlete neither his body nor his attitude, he can be very moody from time to time. That's one of the reasons why he plays for the same club for many years which is "Plüderhausen" in Germany. It's probably the only club which allows him to live his own lifestyle, train only when he really wants to, eat and drink rather unhealthy and so on
But nevertheless he is a really good player, decent feeling and a great backhand but everytime you see him play or talk with people who know him the same question comes up: What more could he have achieved if he would take his sport a bit more serious and live more dedicated to it? There's no doubt he has so much talent and potential but on the other hand it's just his pure personality to play so relaxed and have fun it's doubtful if he could even cope with the pressure and all the standards the other "normal" athletes have or would loose his fun and perhaps even stop playing..
So it doesn't make much sense to debate about this topic we have to take it as it is now and can have fun watching him play (at least on a good day
)