Is getting back to normal life difficult after PhD?
To answer your question, we have to clarify some misconceptions it seems to carry. First, a fixed routine is a staple in most jobs you'll come across. You're going to have to accept this. Even at Google, employees are given the freedom to take time off anytime they want -- but this time has limits, and it's on the promise that they'll return to work for a chunk of hours. The vast majority of jobs, no matter how flexible, will not be lax enough to let you work at a coffee shop in the long run.

The same goes for academia. As a professor or academic, you'll be required to teach, do some forms of public service, and, of course, do research. A lot of things from the first two will be fixed beyond your control in terms of task variation and scheduling. As for the rest, there's some freedom to allot time to tasks as you see fit, but given the amount of work you'll have to do, it will come to be structured in some way or another. 

Second, it's more accurate to say that a lot of people aren't staying in academia after their PhD. The market today is vastly different than it was twenty years ago. Academic jobs are harder to come by, and tenured positions are an endangered species. Most people will find themselves working as adjuncts or lecturers for a large chunk of their careers. And so PhD grads are now more commonly seeking employment outside academia -- industry, governments, NGOs, etc. 

Third, most importantly, no one chooses or should choose a job because of a free schedule. That's far too limiting. Choose a job whose tasks click with your interests, something that motivates you to work. Consider the reverse for your own background: if you hated research, I'm sure that no matter how many hours you were allowed to spend in a coffee shop, you wouldn't have enjoyed yourself or done well.