Q: Why do planets, just like our moon, have their sidereal paths almost the same (with only slight deviation) as that of the ecliptic? Is it mere coincidence? Or is there a better solution?

A: The ecliptic is the path through the sky along which the sun seems to travel during the year.

If you flip your perspective around, that means the ecliptic is basically the path of Earth's orbit around the sun, projected onto our view of the sky.

The question "Why do all the planets lie near the ecliptic?" is therefore the same as asking "Why are the orbits of all the planets more or less in the same plane?" Apart from very distant objects like comets, the Kuiper belt, and the Oort cloud, everything in the solar system is orbiting in pretty much the same orientation and going the same direction around the sun. How did that happen?

Keeping a complex topic down to its most basic level, the answer to that is that all the planets formed from the same protoplanetary disc of gas and dust, so there wasn't a bunch of "stuff" out orbiting in random directions that could form planets with wildly different orbital characteristics. The disc was all moving in pretty much the same direction in pretty much the same plane, so when it all conglomerated into planets, they had to keep moving the same way. //

By the 1990s, astrophysicists thought they had planet system formation all figured out. Nice and simple: terrestrial planets form inside the ice line, gas giants form just outside the ice line, and smaller (but still massive compared to the Earth) form a bit further out, and beyond that, there are some oddballs. But then astronomers began discovering exoplanets that break all the rules: planets with highly eccentric and/or highly inclined orbits, massive planets well inside the ice line. Our solar system apparently got lucky and escaped the chaos that appears to be the rule. – David Hammen