SJS: It is possible, but highly improbable, to make enough money without having a trade. Besides, staying in yeshiva exclusively saps your willingness to go work (at all) when it is required.
In addition, at some point you will have to learn whatever parnassah you want to do, and as we know, at that point the benefits of not working outweigh those of working, and the person ends up being a tzedaka case.