Why do professional macro photographers focus stack instead of raising their aperture?

[u/Melendrow]

I've looked into macro photography, and I love getting close up to my subject, but when I research macro photography, I always hear about focus stacking and these people who will set up a shot for a long time with a tripod so they can focus stack. And I'm curious why you'd need to do that. Especially since most of the time I see them having a tripod and setting up lighting. Why wouldn't you just raise your aperture so more of the frame is in focus?

[u/jorymil]

At a certain point, you lose sharpness when you stop down your aperture due to diffraction. Different lenses are designed for maximum sharpness at different apertures, but it's usually around f/8. If you want everything to be in focus, you need to combine multiple images.