I'm a 64yo male with degenerative disc disease at l2-l3 and l3-l4 from an mri. i have no pain, but i have foot drop in my left foot. how can this be?

Many cuases : Nerve injury. The most common cause of foot drop is compression of the nerve that controls the muscles involved in lifting the foot. This can happen at the knee or in the lower spine. Muscle or nerve disorders. Brain and spinal cord disorders. Multiple sclerosis or stroke

There are several : Possibilities including an injury to the nerve in a region outside the spine such at the level of the knee. One can also have a disc herniation that caused it but the disc has resorbed by time the MRI was obtained. There can be other reasons for a neuropathy or a neuritis affecting the nerve to that muscle group. See a neurologist who can evaluate you and obtain additional testing ie., emg/ncv.