I think you are combining two seperate issues. One, is keeping bochurim in Yeshiva instead of allowing them to go to camp and the second is bochurim going on seed programs instead of going to camp.
Regarding the first problem, the writer has to realize that the number one goal a bachur has to have in yeshiva is to become a lamdan and yarei shamayim. Yeshiva bochurim don’t leave Yeshiva unless it’s for something that has to be done at that moment. Even Yeshivas that encourage the talmidim to do JEP once a week, limit it to that one time. It’s not just bochurim. A yeshiva wouldn’t encourage a kollel fellow to leave Yeshiva to be Marbitz Torah either, untill after studying in yeshiva for a specific number of years. Of course, if there was an immnent dire need, the Yeshiva’s would send out, but otherwise certainly not.
Being that the counselors we have in camp aren’t such a problem that we have to close down the Yeshivas (They are all pretty good, they get intervied to see if they are menchin, which is the most important) the need for seed is much more important. These bochurim go to towns where there are Jews that have no shaichos to Yiddishkeit and can mamash turn around a family.
Of,course evryone has to use seichel; if your son is the type that needs constant suopervision, then seed is not for him.