I can’t speak for the author, but one reason not to use data for logic is that you’ll end up building a (difficult to use, buggy) programming language in your s

I can’t speak for the author, but one reason not to use data for logic is that you’ll end up building a (difficult to use, buggy) programming language in your schema. And if you’re going to do that, why not just use a programming language, which is a lovely way to encode logic? I would turn the question around on you: why would you put this in data? If you have too much boilerplate, just refactor your code.