A big reason for this is the fact that the company behind Steemit.com has been automatically selling around 200K Steem per week.
They have been doing this for years and this has been hardcoded into their platform.
Now, you can imagine what kind of effect this has on the price...
Well, ever since they've hired a new managing director, things have been going in a different direction.
Now they're relying more on ad revenue to pay for their AWS bills and employee wages and they've also been making the Steem blockchain way less resource hungry (due to implementing Mira and switching to RocksDB)
Their new managing director has made a public blog post a while back, stating that they are looking to completely stop the automatic selling of their Steem stake, thus potentially stopping the massive price decline.
Quote
At this point, I feel confident that our expenses will remain consistent, which allows for better budgeting and planning. We currently have nine full time employees and one contractor, so salaries and benefits make up the bulk of our expenses. We cut our monthly lease from $20k to $2k and still do not plan on much travel or other extra expenses that do not help add to the bottom line. The only real variable is the advertising revenue. In order to not programmatically sell Steem each month, we need to bring in enough ad dollars to not only cover expenses, but make enough profit to ensure future stability. Obviously the sooner this happens the better so we can slow down the programmatic selling and ultimately stop it altogether. That has always been the plan and like I said, we are working hard every day to make this happen.
Source: https://steemit.com/steemit/@elipowell/steemit-inc-financial-update