Form is part of it - we'll tend to favor whatever gives us more leverage. One way to fix this is unilateral work. More than just using dumbbells, do lunges, bulgarian split-squats, and one-legged romanian deadlifts. At least, for the lower body. If your left side is lagging that much, do an extra set of everything for just that side (DB bench press, DB bent-over row, DB shoulder press, DB curl, DB french press, etc).
And as a general life-practice, use your left side more. Openning doors, carrying groceries, etc.
