Simple answer is that you're tired and creaky and need time to wake up and warm up. More complicated answer is that your blood vessels are constricted for three hours following a night's sleep. The body also suppresses anti-inflammatory proteins while you sleep. I start slowly every morning. My ankles are creaky and I can hardly push off for 1-2 miles. It takes me about three miles, straight from home, to get going at a decent pace. It helps to take a shower first or walk or drive to a place to run, giving yourself a chance to wake up more. I do my first mile in around 7:15-7:25 (after a quarter mile jog) when I drive 20 minutes to run, whereas I do my first mile in 9:30-9:45 if I just get out of bed and go run. If I spell out the alphabet with my feet and do leg swings, that cuts about 45 seconds to a minute off my first mile. Running shirtless in humid weather also got me about a minute drop. I am sure that going to be closer to 10 than 11 will help as much as anything. Many people drink coffee in the morning and that probably accounts for several minutes.
Here are several tips about remedying poor sleep and stiffness, which I can't vouch for (vitamin D, more fitting pillow, pillow under knees, etc.):
https://health.clevelandclinic.org/wake-up-stiff-and-sore-every-morning-try-these-adjustments-to-make-sleep-swell-again/