This is maybe not true given the right parameters. Typically, people "self-study" on a whim. Probably in the evenings or on weekends. They go for about 30 minutes and then quit, saying, "I feel good about this, I'm going to study like this 3x a week."

And then they utterly faily, because self-study is not one of their pre-established habits.

If you make a schedule mimicking a college curriculum (during the weekday, with a lunch hour, 15 minute breaks, etc) like you would with an actual class, and use the "tuition money" to pay instead for a good desk with ample room for notes and a solid reading light, then I bet almost anyone could do a college education on their own.

It's all mental, and in my experience, mindsets can be changed with the right training. It's like learning to brush your teeth, except you're an adult now.