MTTs are bigger and take more time to finish, but also more profitable. A lot of good regs have roi around 100% at low to mid stakes. Now those ROIs are impossible to get at sng tournaments, but you can play more of them. At one table sng tournament 10% Roi would be considered as fantastic, not even sure if it is achievable, but if you can play 50 of them in one day, you can earn a lot. Variance at sng tournaments is also lower, if you are good player, pretty muh every day you will be earning something. But in tournaments variance is crazy, you can have several losing months before you score big and make profit. All in all, sng-s are constant and relentless grinding, MTTs are focusing and playing your best when it matters.