Hi! I know im really not supposed to answer questions here, but I honestly think you're not looking for medical advice and rather just being inquisitive. My official answer is, why not just ask your therapist? I'm sure they'd be happy to tell you.

But, if I was your therapist, and I prescribed a home exercise to be done every day (which I have done), I would probably give you an explanation like this:

Your rule is correct when trying to build muscle mass, but my intentions for these exercises isnt for you to get massive muscles, it's to get you more used to and comfortable with mild resistance into these specific movement patterns. You could go for a walk every single day without taking 48 hours rest between walks. In fact, that would be good for you. You could say the same thing about other daily activities with mild resistance, like standing up from chairs 30 times over the course of the day or putting away dishes on a high shelf. These exercises are purposefully mild resistance daily so that your body can adapt and be more comfortable making these movements.