Because your employment contract has a non-compete clause

Your employment contract states that if you quit your job, you can’t work for another employer in the same industry for 6 months.

This industry is the only one you know.

This industry is the only one you’re qualified to work in.

What this means is that if you quit your job, you can’t get another job for 6 months.

What this means is that you can never quit your job.

That’s just the way your employer wants it.