Because they don’t plug into Hugo. They’re building bricks that you can use to build your website, well, more like building sections, not individual bricks… Wait, there was a word for such pre-built sections of a building, what was that? Ah! “Modules”!
It may come as a surprise, but Hugo is not Wordpress. It’s not even a direct competitor to Wordpress. Yes, both can be used to build a personal (or not too personal) website, but that’s all they have in common. Different philosophies, different approaches, different means for different goals.
I totally understand the people that used to drive a pickup truck and get confused seeing no steering wheel, but as long as they finally accept the fact that they sit on a motorcycle having the trottle instead of the gas pedal actually does start making sense. And yes, this thing goes much faster and is much easier to handle in heavy traffic. No, you don’t get to haul your new furniture from Ikea on it, sorry; you could, but please don’t.