Very often when $$$n$$$ and $$$m$$$ are variables in a problem, $$$n$$$ will appear first. Alphabetically $$$m$$$ comes first, so why is this the case? For instance when $$$p$$$ and $$$q$$$ are variables, they always seem to come in the right (alphabetical) order.

My thought is that $$$n$$$ is a very popular variable choice, and no one ever uses $$$o$$$ as a variable (easily confused with 0.) so $$$m$$$ is the next natural choice. $$$m$$$ also looks right after $$$n$$$, since it looks like two $$$n$$$'s together. I'm curious if problem setters have other reasonings.