This is not a new trend. It has always been done, in many Yeshivas. In fact, they start very young. Yeshivas start sending bochorim to collect Tzedakah for the Yeshiva at least as young as 8 years old.
The reason is much more than to raise money for the Yeshiva, as important as that is. It is a matter of chinuch. It teaches the importance of Tzedakah for a Torah Jew. Including, importantly, in raising Tzedakah and in giving Tzedakah. This time-honored form of chinuch cannot be foresaken.