Because you’re addicted to the point that you’re physically dependent on caffeine to be able to function. As an experiment try going three days without it and see if you can endure the withdrawal symptoms. It takes around a week to get over the worst part, around a month to get over the worst cravings, three months to feel better and around a year for your body to reach a new baseline. The advantage is feeling well when you wake up, having stable energy throughout the day until you go to bed, better sleep and feeling more relaxed and present in your surroundings.