You hit the nail on the head about the REAL reason the JW religion does not want its followers to celebrate Thanksgiving:..they don't want them associating with non-JW family and friends.
I believe this also holds true for other holidays as well. The claim that these holidays are "pagan" is just an excuse to hide their real intention: to isolate the JWs. The religion is very deceptive in its tricks to trap and retain people!
The religion is afraid that if the JWs spend enough time around people who are not judging them, they may no longer want to be Witnesses.
I wonder if this reason is obvious to many on the forum and those lurking?