It#s a simplification shortcut many people have, but pretty free to play within a spectrum.
Saturation is however a part of "mature" referred art styles which usually mean gritty realism in the consensual sense.
Realism generally has less saturated colors, also a fair bit of gray.
Cartoons and stylized art usually has a lot of saturated colors, but few to none grays.
What you are talking about is a highly saturated accent neutered with grays or subdued colors around, which is something a lot of painters do, but in the end is less saturated than cartoon, but more saturated than a realistic image. And this is measurable.
It's a part of the look. And how much everybody likes a look is purely taste based.
I'd actually be pretty interested in some studies to see what people think looks mature. And not just 20-year-olds, but like 40yo, 60yo, 80yo, 100yo ppl. And little kids. And from different cultures! Some objective testing. If you're saying that less saturated is a industry standard look for maturity, then I can understand that, but I don't think more gray is more mature. It's just more gray. Gives the thing a certain feel, for sure, but not sure I'd call it mature. More angsty? Idk.
Really... It's not about that you see saturated colors.
The difference is how saturated those colors are vs. to how saturated they actually could maximally be.
Sure sometimes if light is right there can be a lot of saturation in realism, but I am not talking about some special exception, rather the general rules of those artstyles. And I am not talking about the tiny saturated apple which is lying in bright sunshine on the huge, rather subdued desk, The desk will fill most of the area, as will a rather grayiish sky and other things about how light works.
I am also not saying more gray is more mature, but it's one of the factors next to proportions and realism levels to describe "mature" as to what most people understand as mature. Don't boil it down to one of the single variables i chose, there are obviously more.
If there would be a better word for this look, I'd use it, but describing a certain effect with visuals is quite hard in language anyways. People refer to it as mature, earnest, dark, realistic, believable and a ton of other more or less fitting words which in terms of semantics can mean a whole range.
And generally I'd be rather good if you'd do some research instead of "wondering", nothing ever came from wondering.
1) Link's Awakening's style was inspired by Link to the Past's style
2) Oracle of Seasons/Ages heavily reused assets from Link's Awakening. The same goes for Majora's Mask and Ocarina of Time. Might have been better to leave both of these out.
3) Though Majora's Mask reused assets, it had much darker themes and style than Ocarina of Time (with exception to the Shadow Temple)
I think you are wrong or don't understand the chart, but let's talk and see.
1) Link's awakening was inspired by ALttP, but it was on the gameboy and had to be made fit to the system restrictions. Whenever you do this inevitably you change the look. There is a reason why something like the castlevania games on the gameboy by a wide audience are considered to "look good" - colors.
An Incorporation of gray always feels visually more realistic.
2) But Sesons/Ages is on the GBC, this means the game generally is more colorful, bc. the normal gameboy initially didn't have colors. Making a fun cute style with no colors is a hard task, and once you pop in colors it looks much more like what you wanted to do.
The DX version of Awakening would be on 1:1 the same level as Ages/Seasons from a visual balance.
3) Majora's mask reused assets, this doesn't change the fact that they bumped up the saturation and shading on link and also not that the new characters they designed for the game generally are all a slight bit more on the stylized side.
Think of the old goron, the goron baby, the deku king family, the zora band, and the gibdo father and his daughter and compare them to the guards, the merchants, the farmers and the carpenters of OoT. MM loved to stylize proportions more.
The ones they overtook from ocarina of time were just made with a more realistic mindset in terms of the design.
The story beats and themes in MM are definitely darker, but this has zero to do with the visual representation / visual art direction at play
Also I myself needed to re-check bc. I felt unsure, but Majora's Mask definitely is a bit more colorful than OoT. There is a much higher usage of purple, but also all other colors are stronger and we find many more saturated colors. While Ocarina of Time mostly builds it world palette from a gray/brown palette and characters mostly use pretty desaturated colors in their designs. The only difference in OoT are some dungeons. The Fire Temple and Jabu Jabu's Belly are the outliners in terms of a colorful, saturated palette. Mos tother dungeons are brown and gray and dark (Deku Tree, Shadow Temple, Spirit Temple, most hallways of the Forest Temple etc.)
In Majora's mask every temple got a ton of strong colored elements in the rooms. Even stone Tower compare dot the Spirit Temple (which are similar in terms of palete and walls) is overall much more colorful due to the incorporation of water, fire, all the saturated enemies and the sky.
A lot of 2D JRPGs also have super dark story themes, but look just cute from the outside. If you look at them and haven't played them, well that informs your opinion. Once you play a game it gets hard to just look at the visuals.
That being said, the chart is only visuals, and doesn't incorporate story beats.
But the story fans had perceived up to this point made the initial perception of WW even worse, bc we got an epic tale with OOT and then a super weird one with MM and WW looked like a pirate adventure with Link thrown in from the first screen releases - and many people also didn't go past those initial looks.