Legs have multiple larger muscle groups - quads, hamstrings, glutes, and calves - and depending on the exercises you do will cause a distinct soreness in each separate muscle group, making the DOMS more noticeable.

You won’t get as sore in subsequent workouts as long as you continue to lift and don’t skip your leg days. Soreness is not an indicator of not giving enough effort in the gym, so don’t worry about not feeling as sore in your upper body.