Line length linters are kinda standard. The goal is to have "shorter lines".

Line length doesn't change just because the font itself is wider.

Seems like the same amount of characters that are each wider would be wider? So you would see less characters on a line with the same amount of characters

Well yes and no. The line would visually become longer, but if we're talking enforced line length by IDE's, say 80 characters, then the line would still be 80 characters long, but just take up visually more horizontal space and so whether or not you see the same amount of characters on a line would become an issue of how much horizontal screen space do you afford for code.