I've noticed the same thing. I'll routinely struggle to understand an academic paper with a notation-heavy theoretical bent, but when I found I had to dig out high school math for a couple 2D-graphics problems recently, it all came back easily.
When you're in high school, you don't realize how much of a gulf there is between Ph.D/MS-level (or even professional-level) math and what you learn in school. The public school system teaches you the barest foundations; there's a gigantic world out there beyond it.
When you're in high school, you don't realize how much of a gulf there is between Ph.D/MS-level (or even professional-level) math and what you learn in school. The public school system teaches you the barest foundations; there's a gigantic world out there beyond it.