It's not that at all. Imagine some popular website is relying on some weird quirk but it works out in modern browsers. They don't even know they are broken, or

It's not that at all. Imagine some popular website is relying on some weird quirk but it works out in modern browsers. They don't even know they are broken, or in what way, and first discovering the issue and then investing in fixing the issue for <1% of readers is a very difficult cost to justify.