So how do you propose they force signing for programs built on top of a VM like C# or Java or scripting languages?

Also, they don’t get 30% of all app sales. All of the biggest non game money makers either allow you to purchase subscriptions and content outside of the store or force you to.

The same way they already force signing for iOS programs. I don't know the details but you can write iOS apps in C#, Java, and Python today so clearly this solution already exists.

No a solution doesn’t exist - all of those solutions compile down to a native executable and don’t run on a VM. Even in a hypothetical unlikely future where the JVM, CLR, and whatever runtimes the scripting languages run on had to be signed (which is not a bad idea), you still would be able to write a program that did whatever you wanted unless now you’re going to say that in this hypothetical future, Apple is not only going to force signing, it’s also going to refuse to sign any executable that can run other programs.

I think they, along with every other major vendor, are consistently moving towards precisely this model. I don't think they will do it soon, but I think it is likely to happen eventually.