concerning the "why" you would have to adress Simon aka "Monty" as he is the creator of CUP;
there is several things missing yet in WAW (which I am flying most often) but as I have said, it is easy to add stuff into WAW; Sometime I just ran into the java wall again and after removing some stuff (mostly aircraft) everything works fine again;
so if you like to have infantry, just grab the necessary mods from here and add them to your CUP install; but as also said, back up your ini files before, that way you can easily revert back in case anything goes wrong...
i am a little bit touchy in this respect because - and dont get me wrong now (it may sound ruder than it should) - with just a little bit of modding knowledge, question like yours could be easily answered by the guys who post those questions...
and do not forget CUP is for free and it has been a tremendous task to put it all together, test it and release it. things needed to be compiled and uploaded so that we guys can get our greedy hands on them...
so if you are missing anything, add it yourself

it can be easily done...questioning why it has not been included in the first place are inappropriate;
btw you could also go the TFM 4.12 way or build your own Modact modded game...
thats the beauty of the modding world here...the never ending possibilities...