They make these changes and roll them out. They look at the numbers. They see that 5% of their users (those on older hardware) spend 20% less time on the site. They see that 20% of their users are spending 50% more time on the site. They file a ticket about the drop in engagement for older devices. It goes into the backlog. Next sprint/quarter rolls around, they see a couple of options. One is to speed up the site on old devices another is to add a new feature that they estimate will increase engagement by another 20%. The second option seems to increase their bottom line more, so it gets funded and the old device support stays on the backlog. Repeat cycle.
I can guarantee that at any sufficiently high traffic site they don't use developer hardware as a benchmark. They see the numbers, they know its slow for you and they make a conscious decision that you aren't worth the opportunity cost of new features.