Kids are trusting, they don't believe their parents would ever lie to them. So they see how happy it makes mom and dad if they dedicate their live to Jehoobie and they go ahead and take the plunge.
The WT society is consciously pushing this effort to trap children into a lifetime contract with the cult. If they effectively suppress the normal thinking and exploration that happens as a teenager and young adult, they have a servant for many decades, if not forever. They effectively pair this policy with their evil shunning doctrine, making the emotional pain of leaving intense for any person who contemplates doing so.
And the primary reason for doing it is because they have seen how poor their retention rate is over the past 30 years.
Its evil. They are emotionally enslaving little kids so their cult will survive. Dickheads.