It's not though. The only people that can apply it are the supreme court and the only time they'll apply it is when precedence and the letter of the law goes against their own political ideologies. In short, it's lazy judicial activism.

It's anti-textualist, anti-originalist, anti-legal theory. It's a rule that the Supreme court has to invoke to achieve their objectives because they have no other avenue. The law was clear, the intent clear, and what congress desired was clear. Major questions should be solved by congress passing a revision to the law. The supreme court invoking it robs congress of their power because "we know better".

The reason it's such a bad rule is no lower court or litigant can really invoke it. It is only something the supreme court can use because it's undefined what qualifies as a "major question". Boiled down, it's "we don't like the law congress passed but we can't come up with a constitutional, textual, or historic reason why that law or it's application is invalid".

They would not use "major questions" if there were any other legal reasoning to go to.