You are not alone in your response to this type of surgery. Studies show that a number of patients do not attempt jumping or squatting activities after knee surgery. This is true despite the fact that they have good range of motion and near normal muscle strength in the operated leg.
Fear if reinjury may be part of the problem. But there may be other factors to overcome as well. For example, a natural decrease in activity level over time may leave that leg weaker, less stable, and not fully rehabilitated.
You should schedule a follow-up visit with your surgeon. Talk to him or her about your situation. See if a short course of rehab with a physical therapist might be appropriate to get you over the hump.