The unicyclist on the left is saying the bicyclist is only riding a bike because they don't have enough skill for a unicycle. The unicyclist on the right is saying they can't learn to ride a bike because they've spent too much of their life riding a unicycle. It's a dig at people who don't want to switch to memory-safe languages like rust.
I am both the left guy and right guy. If you can't program without using a memory safe language, it's a skill issue. But I also don't want to switch to rust because I like the challenge of manual memory management. (Also rust's syntax and semantics looks like it was designed by a monkey attacking a typewriter.)