I think Steem changes in relation to bitcoin because of larger buyers buying/selling using bots as part of portfolios. The relation of posting rate to token value shows that people are using the platform to make money and the lack of social feature development means that in the market place Steem sites are not competitive on their own merit in that regard. People need to be motivated to use the sites with or without rewards, otherwise they will just post elsewhere or do other things when the token value is low and they can be rewarded for their time more effectively elsewhere. That's my opinion anyway!