Aaq, it’s true that yissachar and zevulun have the same schar, but how many baalei batim have a total Y/Z relationship? Most, do not. Especially those who deride kollel. How will they stack up to talmidei chachamin?
Also, my rosh yeshiva says bshem the gaon that Y/Z having the same schar only applies if the Z tried his best to bea Y, but hashgocha led him to have to work. Otherwise it’s not logical that one can just spuriously decide that he doesn’t want Torah.