Because they're unsure, nervous, playing with borrowed $, seeing significant double digit downsides on a bad news release with other companies, reading bashers on this MB, weak hands, faint of heart; how many more scenarios do you need to hear?
Are institutions selling? This stock is perfect for manipulation. It's in the right (wrong) sector for wild rumors, & high speculation. Quite frankly, if an investor, I said investor, not a trader, believes in what SRPT has at this moment in history, he should continue to hold & IMHO, buy more on any retesting of the mid $25 price range (if it retests).
You asked a question, here's my solicited, unpaid for answer.