There are a few different reasons why short selling may be allowed on some platforms but not others. One reason is that short selling can be disruptive to the market and can lead to increased volatility. Another reason is that short sellers can sometimes manipulate the market by driving down the price of a stock in order to profit from its short position.
Platforms that allow short selling typically have rules in place to try and prevent these types of disruptions and manipulations. For example, they may require traders to borrow shares before they sell them short, or they may limit the amount of shorts that a trader can have in a particular stock.
