Since Netflix's OpenConnect boxes are held in the ISP's own network, for exactly the reason of lessening upstream transit/peering costs and bandwidth, why do they need to also limit the bitrate? The content is basically already on the ISP's LAN and streamed to local (customer) connections. With the absence of a Netflix discount I've dropped down to the 1080p 2 screen package and saved 25%. Pointless paying full whack for reduced quality.
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Possibly because Netflix may not have the capacity at every ISP to fill all it's members requirements at that ISP at the moment?
It may be that not every ISP has those boxes "near" to the customer - for example some might have them in their main DC's but then have multiple links out to more regional facilities (IIRC how UK ADSL operates, and if you've not paid for a good enough link to a town and it's been near capacity during normal times but you've been putting off an upgrade because of the cost, then suddenly you've got a massive increase in use...).
Not every ISP has netflix boxes held in their DC's at all - I know it's hard to believe but IIRC even in the UK at one point the BBC were getting complaints about the bandwidth the Iplayer used*, despite offering similar local content servers. The reason being it costs money to provide the space in those DC's...
And the fact that the problem seems to be in some of the EU ISP's (not UK), many of which are cable in which case it is the internal bandwidth that is almost definitely a problem given that cable typically shares bandwidth between users on the "local" run to the UBR, something that used to cause massive issues for NTL/BY/VM in the UK especially in "student" areas during university term times at peak hours.
IIRC it was said right back at the start of this that the reason Netflix has put the changes in place was because of bandwidth issues with EU ISP's, given that most/all ISP's tend to build their networks on certain usage assumptions I'm going to bet that many of the older ones (and some of the newer ones) probably were not built with the thought that people would be streaming HQ/UHQ TV in huge numbers throughout the day, whilst many more were trying to work from home and do things like video conference.
*I think from some of the cheaper no frills ISP's that popped up to supply ADSL who then got upset that customers used more bandwidth than they did on 56k.