Just A Question About "Spirits" In Runterra

Why do some "spirits", which I will call them for the remainder of this discussion as there still lacks an official name for them, have to use emotions and feelings, or some other outside force, to maintain themselves, such as Janna and Evelynn, while other spirits, most notably the Yordles, lack this characteristic?

In the lore so far, there has been very little given on the spirit realm or otherworld, or whatever Riot decides to call the plane of existence that these "spirits" come from. From what we do know, it overlaps with Runeterra, not unlike the Void, and, as shown in Shen's lore, is accessible by humans, with spirits being able to freely walk between the worlds. From Lissandra's biography, it says, "In a time long forgotten, before the sands birthed and then swallowed Shurima, beings of old magic freely walked Runeterra. The borders between the mortal realm and what lay beyond it were hotly contested." indicating that, possibly, there was a time when there wasn't some invisible barrier between the realm, though whether this is referring to the realm of the Celestials or the Void, and it's relevance to this discussion is a conversation for another day.

My working theory so far is that spirits such as Janna, Evelynn, Tahm Kench, and others, have to maintain themselves because, though they may have come from there, they don't live within the spirit realm. They live in the waking world, and in order to keep their physical forms and powers, they have to feed off of a concept, specifically, the concepts and emotions of the human psyche, such as hope, fear, mercy, lust, and anger. Their relationship with humans can be either symbiotic, as in the case of Janna, or parasitic, such as the case of Tahm, and depends strongly on what concept they choose to feed off of.

However, where does this leave nature spirits such as Maokai? Well, I have another theory for that, which coincides with the first one.

While some spirits may choose to attach themselves to an ideal of humanity, which can give them incredible power, influence, and reach, it also leaves them quite vulnerable, and their power can be lost as quickly as it was gained, as shown in Janna's biography after people stopped believing in her. Some probably seek a more stable, secure way to exist in Runeterra, which is why, instead of attaching themselves to a concept, they attach themselves to something physical and/or constant, such as a place or object, or just a part of nature, such as trees or the weather. The trade off is that, while their forms and power are easier to maintain, they're limited in what they can do and where they can go.

Why spirits such as the Yordles don't have to do this is simple; they live and remain in the spirit world, and thus don't need to "maintain" themselves.

Again, this is all just my personal head canon, and I would deeply appreciate if a Rioter could help clear the air on these "spirit" champions.

This is just a little sidenote, but I don't know where Kindred would fall into all this. They're the embodiment of something primal, death itself, which has existed for as long as the world has existed. They're not on the same power level as the Celestials, like Aurelion Sol, but they're definetly higher up than spirits.