"Many investors sell short because they expect prices for a particular investment security to fall. For this reason, an extreme amount of Short Interest can mean that the market sentiment about an investment security, or about the market, is pessimistic.

Some contrarian investors may interpret extreme Short Interest as an indication that market sentiment is too pessimistic, which can be interpreted as a bullish signal. Another reason some investors bet on stocks with heavy Short Interest is due to the knowledge that eventually those short sellers will have to repurchase the stock, meaning there's guaranteed buying interest in the future."

source: seeking alpha

https://seekingalpha.com/article/4450371-short-interest