Why does the OKLAB color space look so jagged?

I understand that color is a 3D value, since all perceivable colors can be created my independently mixing 3 base colors. That naively gives us a color space shaped like a cube (like SRGB).

I also understand that every color space needs to remove colors from the ‘everything’ color space due to technical limitations. This is usually represented by ‘cutting out’ a triangle from the following representation of the ‘everything color space’.

BenRG and cmglee, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Even accounting for distortion of the color space (think Mercator projection), I believe there should only be three curves that cut the solid color space. Hover, in the image of the OKLAB color space there are 5. Why is that?

And why is the ‘amount of height’ they cut from this supposed triangular prism so different depending on hue?

The image is taken from the OKLCH Color Picker & Converter by Andrey Sitnik & Roman Shamin. https://oklch.com/#0.7344,0.1025,272,100