> They should be making their website’s code more accessible to legacy devices.

If there's an iota more work involved, the analysts have no reason not to defer to analytics. Anything less than ~1% gets dropped. So there goes your ES5 build.

"Accessibility" in the screen reader sense is additional work done to support a low-usage audience, but because it has legal implications it has much more weight.

I guess it would take someone using older tech winning in court for this to be given greater consideration. But that seems unlikely because people who use older tech are not a protected class.