Because "this is X for Y" is technically one sentence but it needs a lot of work to decode. If you can deliver just a sentence, it should also be just a sentenc

Because "this is X for Y" is technically one sentence but it needs a lot of work to decode. If you can deliver just a sentence, it should also be just a sentence of thought to parse. Instead we need to think about what is X, what is Y, substitute the variables, and now we're juggling a paragraph of incoherent thought. Whereas a "Do this, and that happens" doesn't need any of that.