Besides it being another way for them to use something for control, and create the illusion of "us and them", it also probably has financial reasons to "paganize" holidays specifically. If the members of your org are not spending countless dollars on Christmas, Birthdays, Halloween, and all the yearly holdidays with their commercial value, then this money can be given to the borg.
Its quite brilliant, if ya think about it. Tell the sheeple, " do not celebrate, and dont give your money over to paganism, but hand it over to US". Forget about using it to give your children a happy childhood. No, the children dont need that, the WTS needs your money, instead. So, in answer to the OP's question, the reason they pick and choose, is probably BECAUSE of the very money itself.
The most hypocrytical aspect of the WTS, and paganism, is also the very fact that the WTS's roots themselves ARE pagan. We see the watchtower symbol as their main symbol, yet, as brought up earlier, that symbol itself has tremendous pagan origins. The massonic symbols, that were plastered all over the original literature, are all pagan in origin. From the cross and crown, to the watchtower itself, all pagan.
Its again, just another example of them picking and choosing based on convenience and neccessity.
