Even people "born into" a religion are responsible for their own decisions once they become legal adults. So anyone that gets baptized after reaching the legal age of adulthood has chosen this religion.
Still. you're right it's definitely a choice - but a different from that of the choice to convert when you're an adult with no JW background to normalize the choice.
While the born-in does make a choice, it is completely different from someone that comes in later so I have to agree with Steve here. Also, most born-ins end up baptized before they are legal adults because the religion pushes child baptism to hook 'em in, that fact can't be glazed over either. Personal experience, I got baptized as a teen because I was tired of everyone asking me when I was going to do it (most of my friends had been dunked already). I honestly didn't want to do it, but felt like I didn't have a choice.
For the OP, people love to be part of a community and that is exactly what the JWs offer; everything looks great in the beginning.