Dolphin only using about 20% of each CPU core

[OverMighty]

While I was playing Mario Kart Wii on Dolphin 5.0-10648 on Linux, I ran htop and I noticed that the CPU usage for each one of my CPU's 4 cores was around 20%, but the game was only running at 35 FPS:

https://images2.imgbox.com/b0/5f/ykGN4NvW_o.png

Why isn't Dolphin using more of my CPU to increase emulation speed?

My PC's specs are on my profile if they might help you figure out why.