And that's exactly why birthdays and all other common occasions that bring families together are forbidden. New recruits stop being with their families. This creates a rift and resentment in the family.
Bingo!
JWs often claim the main reason they are not a cult is because they are not isolated from others by living in a commune. They may not live in a commune but they are as isolated as anybody on earth via no birthdays, no mother's day, no father's day, no Thanksgiving, etc. These are the very things that bring most families together.