I wish someone invented and actually sold tires which can't go flat. I don't mind if it makes the bike somewhat harder to ride. For short-distance trips (intra-city) this should be no problem, and could perhaps even save me a visit to the gym.
You think that because you don't realize how much harder it is. Like it takes significantly more power, turns much worse, and is much less comfortable.
Solid rubber tires exist though you are welcome to try!