This lack of consideration by many websites for my slight visual impairment is a pet peeve of mine, so I was deliberately stereotyping the developers. I'm sure the reality is much more nuanced. E.g.

a) the web layout software they're using doesn't work well with larger fonts. Nobody can realistically design today's websites by manually writing all the HTML, so when the tools have limitations, then the website has limitations.

or b) the designer has a lot on his plate. He needs to do ten things, and nine of them should have been finished last week. He's only got enough time to get things 95% right, not enough time to worry about every single border case.

or c) as mentioned in other comments, the designer is being rigidly constrained by management expectations of minute details of site appearance. Those constraints at default font size are incompatible with perfect rendering at larger font sizes.

I'm sorry if you were offended by my colorful choice of words. One of the nice things about Hacker News is it's generally a high-content low-noise place where people don't flame or troll.