I have a theory why, but it's my personal opinion.

I think that because the supply of STEEM dollars is increasing with each UP VOTE or block of content. The DEMAND of people buying STEEM dollars do not keep up with the SUPPLY of people wanting to sell their steem dollars, to obtain an income from their content.

I however think that if the STEEMIT community would consider to vote that ADVERT be placed on STEEMIT, that is paid with STEEM DOLLARS, the DEMAND for steem dollars will INCREASE. If demand increase so does the VALUE of steem dollars.

Just my thoughts...

@sacryptocollect