Why does Kibum need acting lessons?

Well, I know that Kibum really wants to act but why does he need to undergo acting lessons? He's good already. I dont know if Siwon took acting lessons but he already got a lead role in a drama. Cant Kibum do the same thing? or Siwon is just a better actor than him? I'm really confused.

I also conclude that if Kibum will not be given acting lessons he might also do what Hangeng did, terminate his contract with SM. Because we all know that he (Kibum)just joined the company to act.

How about you,what do you think?