Not so seem argumentative or anything, but again that is based on perception. Nothing happens "because", not even magic. Nearly every world has purpose behind magic. Let's take an extremely popular one: The Forgotten Realms. In this creation, magic may not be completely understood but has constant application. It has to be researched and learned, there are laws that nearly always remain the same, and it has various sources.
Even if you don't understand why a rock moves because you tell it to, some force is making it do so. Typical magic is based off a force beyond our understanding just like the "Force" in Starwars, which by the way is basically watered down magic. It's still there. In the end, it's not really different from someone rubbing flint together to make fire and wield it as a weapon but not know it works.
And both magic or technology can be either linear or none linear, depending on the writer. In reality, science is pretty linear. However, so is most magic in fiction. If it wasn't, you'd never be able to have practiced magic; every time you attempted to cast a spell it would do something completely unpredictable. Instead saying those words keys a process which may not be known to you that has nearly the same result every time.
The very fact that you can say "wingaudium leviosa" and expect the rock to float every other time is because it is linear. The reasoning may or may not be clear, in fantasy it's typically 50/50 between worlds where magic is a force that can be learned and researched and worlds where magic is wild and untamed, used by those with natural talent and never completely understood. In all cases, it's still a force by it's very definition.
"Just because" systems usually never work, it shows lack of thought in a writer and is very unrealistic. Humans never buy it. You woud be hard pressed to find a magical world where magic is explained as "just because" (compared to just unknown and mysterious). Even if you did, I'd bet a decent sum it isn't well known or remotely popular.
