The point of ISDS isn't that it magically constrains the governments in question. It's that the price of choosing not to comply with a ruling is so high (typically, abandoning the entire free trade agreement and reverting to WTO rules) that it's a serious barrier to a government actually doing that.

That doesn't mean we should fear the bogeyman, since in reality such provisions have not been unusual in previous free trade agreements and the most notable ISDS cases were ultimately failures for plaintiffs like Big Tobacco. But even though results have usually gone the right way in the past, they have still cost the governments involved a lot of time and money to fight the case, and that alone is grounds for asking whether the ISDS provisions are a good idea.