The real purpose of sending your kids to eretz Yisrael for a year is because you’re sending them to eretz Yisrael for a year. Our people have only been able to dream for the past 2000 years that they would be able to come here and now you can give your child the chance of living here for close to one year. Every four amos is a mitzvah here and there’s no kotel or kever rochel just one bus ride away, no matter where you are in Brooklyn.
Yes, some of the boys and girls who come to Israel get into trouble. There’s no way to know that they wouldn’t get into the trouble if they stayed in the US but I understand that some parents are nervous. (Also, if some kids have it in their system, it could be good for them to get it out before they get married. )
There is much less materialism here. Even the people who are fancy here, can’t indulge as much as they would in the US. It’s nice for the kids to see that they can do with less and to see that people are willing to live with less in order to be here. It’s also beneficial to your children to see all different types of Jews and to spend time with other families and learn from them.
About girls specifically, the girls spend 12 years in school just learning for the sake of good grades and they are probably going to spend the first few years of marriage working like a dog so their husband’s can learn in kollel. The least they deserve is one year dedicated to their spiritual growth with all the hashkafa classes that their 12 years of BY didn’t offer them. Once they get married and have kids, there will be no time for trips so this is hopefully their last chance at exploring the world and eretz yisrael and at being able to enjoy themselves.