Why?
On a micro-level, the fundamental business is a bit shaky. It's burning cash like crazy, and it's unclear if can turn a profit. On a macro-level, comparable stocks have been tanking lately. 
This chart from Bessemer Venture Partners shows how far a basket of "cloud" stocks has fallen from their peak. The cloud index tracks 37 publicly traded companies. 
The cloud companies are still outperforming the broader market since 2012, but the trend doesn't look great. It helps to explain why Box's bankers may have struggled to sell the Box IPO.
bvp cloud index
Business Insider