Why is that, in a non zeros roulette, after the ball lands on black 8 times (or more), then the chance of landing on red the 9th time is still 50%?

Regardless of how many times it has previously landed on black, when it comes to the next spin there are 18 possible red slots and 18 possible black slots for it to land in. It’s as simple as that – the opportunities for red and black are equal, so the probability for each is also equal.

Since it is a near-memory-less system (unless it is rigged; however, in theory every electro-mechanically built system is not perfectly memory-less; but that’s a story for another day) and therefore causality cannot be expressed.