Sure, but this being the web and the font choice literally being one line of CSS it is not that hard to make things slightly better for everyone involved.

Even more so when a lot of the blogs I have in mind also try to appeal to a slightly broader audience than just the nerds used to monospaced fonts.

> Older research papers were often written with typewriters, leaving blank spots on the page for formulae,

Well, if you read them on paper it is a slightly different story. That is one of the main issues, fonts work differently on displays than on paper.

If you mean that you read these scanned papers, then I'd say that your argument mostly boils down to you being used to it by now. People can get used to a lot of things, to the point that they think they prefer it out of habit. That doesn't mean that they are actually better and can't be made better for other people starting out who are not used to these things.

Where monospace was pragmatic for the typewriter era because of the limitations of the technology, proportional is the pragmatic _and default_ styling of the web.

Choosing monospace today for prose is an opinionated, and in my opinion suboptimal, choice.