Steem is one of the leading platforms for the creation and usage of applications. Running these networks cost money. There is development, employees, servers, and a host of other costs that come from running a business such as this. Most are operating as thinly as they can but one cannot eliminate all expenses.
One of the potential largest seller of Steem are witnesses. According to @aggroed post, server and electricity cost break even at 3 cents. Even if we assume it 5 cents, witnesses can still sell Steem until it reaches 5 cents.
Right now a top 20 witness makes 110,000 steem per year or something in that vicinity. Each Steem is worth 20 cents right now. So, witnesses are earning $22,000 per year. I run two witness nodes (and pay for half of the minnowsupport rpc, but that's separate from this). My nodes cost $120/month each. So, that's $240/month. So, that's about 3k per year. The price of steem has to get down to 3 cents before I start asking myself "do I even want to run a node here?" Maybe some of the backup witnesses would stop hosting Steemd by 3 cents, but I don't see enough leaving to stop the chain until Steem hits 3 cents.
If all witnesses (approx 200) earn 3M Steem (110Kx20+800K= assuming rest of the witnesses earn 800K), and sell 80% of them, then it is 2.4M Steem selling pressure per year. Though are active and work hard for the Steem chain, but they may not have investor's mind-set (ROI or speculation), therefore, can keep selling at low prices.
It is not their fault. It is the fault of vastly STINC's and large shareholder's not doing enough marketing for Steem to bring new investors.
I am 100% agreed with 
RE: Why STEEM Drops More Relative To Other Cryptocurrencies