What happened to all the unavailable classes?

Hi everyone,

I haven't played maplestory in a while but i decided to try out again. I planned on making an Aran since i never got the chance to try it out but it seems to be unavailable as well as a bunch of other classes. Could anyone explain me why this is. Is it part of the story? or are they reworking/fixing some classes?

Thanks in advance, tuna