One of the most underrated aspects of squatting is the role that your body's core plays during the movement. Despite the squat being an obvious leg workout, you will never continue to add strength without a strong and stable core. People ask me all the time why I don't squat with a belt, my answer is simple. "I want to strengthen my core". It's true. You can get abs from squatting.
The amount of stress and tension placed on the core while squatting a heavy load is just as exhausting on the body as all those crunches you're doing when you train abs. Now... Im not telling you to stop training abs, but what I am saying is to be smart when you decide to use a belt or not.
A belt can be a great tool, but it's important to know its true function and how to use one. If you do decide to use a belt, realize that your belt doesn't really brace your back, but rather, gives your stomach something to brace against. While squatting, you need to push outward against the belt with your stomach, this increases stability in the movement that you otherwise would not have.
Please do not become reliant on a belt, be confident in the squat under any circumstances, and your legs are sure to grow! (And your core)