Actually most majors do not require post-grad internships. But voluntarily doing summer internships in the domain of your major is a great help in getting that first real job after graduation. So in doing that you start off with some of that "practical learning experience."
Do not treat the summer jobs lightly. First, they're tough to get because everyone who understands their importance will be vying for the same summer jobs. have a slam-bang resume' that sets you apart from all your classmates for example.
Second get a letter of recommendation from your summer job boss. You'll append that to your resume' for your first job hunt after graduation. That will help set you apart and above your peers who are also vying for that job. From experience, I know some bosses are not very good at writing recommendations. Be relentless, but kind, and insist on that letter.
There are of course some majors that do require post-grad internships. Clinical psychology, for example, requires 2000 work hours in a clinic in order to be certified to practice in California.
But the number of majors requiring post-grad internships is small compared to those that have no such requirement. To my knowledge, none of the STEM majors requires post-grad internships for example. But, from personal experience, summer jobs in STEM enterprises can give you a leg up coming graduation and your first job search.