Why older people don't want to get off the couch

During the last few years I've noticed that my limbs are getting stiffer. I cannot manipulate my body like I did when I was in my forties. I used to leap off the bus, but now I hold on to the rail and slowly lower myself to the street. Note-If you ride the bus, you know that the curb is usually many inches from the back door. I personally like to debus from the back like the sign suggests (am I still trying to be a good girl?). Plus, I sit towards the middle of the bus so as not to get evicted from my seat for seniors and wheelchairs. Advanced planning is your friend when frequenting the transit system.
Back to the subject at hand. This aforementioned stiffness is why older people don't like to get up from the couch.