Bochurim don’t pay to learn. The Yeshiva asks parents to help cover the costs of the institution that’s helping the parents fulfil their job of teaching their son Torah, providing him food, board, and a heated/air conditioned building etc etc. At a fundraiser for a Yeshiva I once attended, the R”Y said tuition only covers about a third of their budget.
A kolel doesn’t pay their members to learn. The same way they provide a building etc for them to learn in, so too do they look to provide for their living expenses. Very different perspective, while it’s the same Torah.