What i don't understand as neccesary is the 21 block producers. Why can't this be 210 block producers? I understand that much of it is about ensuring absolute best latency, to create the fastest blockchain, is there any other reason?

The problems here are two things: Centralization in wealth of the system as well as Centralization of nodes (I know this aspect is greatly debated, having to do with mining pools and all that).
To me this is the biggest issue with EOS, Steem and Bitshares. As a regulated system maybe it's fine, it will bend to regulation much more easily than other blockchain systems. There is plenty of room for success with this model, but I do think it is giving up on some of the most disruptive aspects of blockchain.

EDIT:
This is an honest question, i'd love some discussion around this if anyone has some insight.