One source hypothesized the reduction in power-down time from HF-19 encouraged lots of people to start cashing out and the downturn could continue for two months. Of course, crypto is taking a hit all across the market so there are other factors in play but that might be one explanation. Hopefully the influx of new steemians (over one thousand per day I estimate) will prop up the demand for STEEM as we eagerly power up every little bit we can get our hands on.

EDIT: I'd add another source's hypothesis that the summer season is encouraging people to cash out to fund "fun-time" expenses so it could be a bit of a seasonal thing, too.