Because unlike prose, we don’t reason about code in terms of words, sentences or paragraphs but rather in terms of statements, lines and blocks. Navigating between visual lines vertically makes sense when navigating in code. And to optimize this kind of navigation, monospace fonts are the best choice because where your cursor lands is predictible. It also brings cool features such as block selection which you can’t implement properly with proportional fonts.
I don't quite understand this. I've used proportional fonts in PyCharm and other editors for many years, and vertical navigation and block selection work fine.
For me legibility is more important: unlike prose, for code it's much more important, what's written in those lines, and monospace fonts sacrifice legibility for columns. And no, monospace fonts can't make cursor land where it needs to, because the destination can be anywhere on the line.
Because unlike prose, we don’t reason about code in terms of words, sentences or paragraphs but rather in terms of statements, lines and blocks. Navigating between visual lines vertically makes sense when navigating in code. And to optimize this kind of navigation, monospace fonts are the best choice because where your cursor lands is predictible. It also brings cool features such as block selection which you can’t implement properly with proportional fonts.