"pretty rational" is an overstatement. There's alot of new math and ways of thinking and rational and intuitive are the two words I would never use to describe it.
.. and the word "negligible" bothers me in that context.. Quantum effects simply does not happen on larger scales. It's not that it's too small variations so we can't see them, it literally does not happen on any small un-isolated particles.

How about the many worlds interpretation? Doesn't it state that a possible explanation for quantum effects only happening observably on smaller scales because when it happens on bigger scales it literally creates parallel universes?

I only know about quantum physics on a hobby level, please don't kill me if that's wrong.

kinda and not really.
Quantum effects don't happen on larger scales because for quantum effects requires a certain level of uncertainty or "unknowsness". The particle in question must be unobserved to be in that quantum state called a superposition where it is both a particle and a wave-form at the same time (particle-wave duality). If we know the, say, position of a particle at any given time, we've measured the superposition and it collapses to a particle and only a particle. We can't measure the position of wave-formation, so of course it's a particle. If you drop a pebble in water, exactly where is the waterwave?
[sidenote: Quantum effects have been successfully tested on larger scales as well, up to molecules of ~100 atoms if I'm remembering correctly. Just requires the right setup. ]

What your saying about the multi-verse theory (or many worlds interpretation) is a currently valid theory, and one I myself hope and believe to be true, but it doesn't explain why it quantum effects don't happen on larger scales. It, like you correctly say, states that every time a particle has to choose from a superposition, it creates two new universes, one with each outcome of the superposition. This however, is really really hard (if not impossible) to prove and will probably remain a theory for(ever) a long time.

\rant sorry