[buckeye]

This is purely anecdotal evidence but I'm not so sure Netflix's reduction in bitrates has been applied to the UK.
I'm still getting their full bitrate on UHD material today.

Pip's mention of CDN's is a bit of a red herring, all the streamers have their own CDN's or leased ones, for example BBC Iplayer has at least two leased CDN's.
ISP's optimise their infrastructure to provide a balanced delivery of all internet services,
however its not unknown for the likes of Netflix to pay to have their own infrastructure within an ISP's hence the furore in the US over the abandonment of net neutrality rules.

In the grand scheme of things whether a streaming service does or doesn't reduce bitrates or give a lesser service than we have paid for is irrelevant,
stay safe everyone here.l