Jail and prison are not the same thing. Jail is for light crimes - most people in jail leave every day to go to work, and then return to jail when work is over. It is easy to run, but odds are they will catch you (they know your family, job and friends...). It isn't uncommon for the windows to open without triggering even an alarm.

Prison is a level higher. You start out in a more secure setting where it is harder to do anything without getting caught. (if you only get 1cm of tunnel built it doesn't do you any good). If they suspect you are going to pull anything they move you to more secure prisons where you are watched closer.

You might be smart, but there have been lots of smart people in prison before you with nothing better to do than dream up every possible escape plan. They are gotten good at detecting and preventing them over the years. In short odds are against you getting out successfully, and the attempt will earn you more time in prison.