The kids leave for other several reasons beyond what has been stated by others in this thread:
1. They look at the older generation some of who were also raised in the truth. Most of these people have little or nothing materailly. They were deprived of a college education, and they ended up doing some funky job somewhere, or became one of the legions of office cleaners (no offense meant to any one). These people have little in the way of sustaining life after they grow old enough that they can't work. No pensions, never made enough money to have an accumulated wealth, insurances, etc, they were told from the time that they were kids that the end was coming soon and they didn't have to worry (I know scores of them. I grew-up with them and see them weekly). Now they do, and the young ones see it. I never drank the Kool Aid on this subject.
2. Many of the young ones have been brought up in homes that were materially deprived because their parents were unprepared for life by listening to the WT Society. The young ones are not going to repeat the performance. They want better, plus because of this they probably have to take care of their Parents.
3. Today, cars cost 20-30K on average. A house costs $ 500K in a suburban area, etc. The kids realize that they need an education or be trained in something good to be able to earn enough money to live. You can't wing it anymore. They are smart enough to realize that if they Pioneer and do nothing to further with their lives in a secular sense, their ability to earn a living in a rapidly progressing world is slim. If they wait for the end to come as their parents did, they won't be able to live an adequate life. Thats just the stark realities of life.
4. Don't forget, you have to earn enough money to put some in the box at the KH. Somebody has to pay for things.