I don't have any sources, but squatting doesn't necessarily stress the hamstrings as much (like a typical medium stance deep squat) so you might develop and imbalance where your quads are too strong compared to your hams. There are other kinds of squats that put way more stress on the hams, though, like box squats, very wide parallel squats (like some powerlifters prefer) They stress the hams more because of less knee flexion and more hip flexion.
