STORJ is more expensive. So they can easily gain more people to provide storage space. The problem is getting more customers. I'll have to research their business models more. But Sia shot up like crazy, there will be some positive sentiment. Because of SIa's price increase, their service cost has also gone up. STORJ is also on Binance. That's a big plus.
https://www.reddit.com/r/storj/comments/7ommsh/why_would_i_use_storj/