Because when we look across to a distant mountain, there is more blue above the mountains far away. There is no blue seen through to the mountain, only more blue above and around the mountain.
Prove it.
There’s no excuse for this.
There are 2 quite simple ones:
1 - You are lying. You are just saying whatever result you want to be the case with no concern for reality.
2 - You are unable to tell as you have no valid reference. Especially if combined with your wilful ignorance where you intentionally don't go looking for any evidence for this claim because you know it will show you are wrong.
The simplest and perhaps most well known example of that is the colour of this dress:

People couldn't agree if it was white and gold or blue and black.
This is because different colours appear different in different lighting conditions, so your mind naturally tries to adjust.
And the clear proof of that is in optical illusions, where this is specific for the dress:

The "blue" in the yellow region is the exact same colour as the "white" in the blue region.
It is the same colour, with the same RGB values, so the same light coming from them. But your mind interprets them differently depending on its surroundings.
Likewise, it appears in illusions like this:

Here you are asked which is darker, A or B.
In reality, they are the exact same shade. But because you perceive B to be in the shadow of the cylinder your mind interprets it as being lighter than A.
Yet again, they are exactly the same.
And the same happens when looking at things through the blue atmosphere.
Your mind naturally tries to white balance and can easily ignore some of that blue.
If you would like an example of a far away mountain, then consider these three possibly edited photos:



Without trying to look it up to find the reference photo, can you tell me if these photos have been edited and in what way?
And just to clarify, it is entirely possible that all three have been edited in the same way but to different extents.
Once you provide the answer, or show your dishonesty by refusing to, I will provide the original and show that you are wrong.
If the air is blue, it would be blue where most air exists above Earth, at the surface and above the surface to 30000 feet, where 85% of the air exists.
Stop just spouting pure BS.
You are quite literally just making numbers up.
Just look at the comparison:
Between the Earths surface and up to 40000 feet altitude, is over 85% of the air above Earth.
vs
If the air is blue, it would be blue where most air exists above Earth, at the surface and above the surface to 30000 feet, where 85% of the air exists.
Make up your mind.
Just how much air do you think is at these various levels? It can't be 85% at both unless you are saying there is no air from 30 000 ft to 40 000 ft.
More importantly, BOTH NUMBERS ARE PURE BS!
The amount of air above any point is based upon the pressure.
1 atm at ground level has 100% of the air.
At 35 000 ft, the air pressure is roughly 0.24 atm, meaning 24% of the air is still above, with only 76% below.
At 40 000 ft, it is closer to a 20-80 splt.
It is only at 45 000 ft that it reaches that 85%.
Ref:
https://www.engineeringtoolbox.com/air-altitude-pressure-d_462.htmlAgain, this shows you are willing to spout whatever dishonest BS you want, to pretend your fantasy is true.
But more importantly, as explained to you repeatedly, there is a difference between it being blue and you being able to notice that blue.
Even with only 15% of the sky being above, looking up you just have that blue light coming down.
It isn't mixed with anything else to make it hard to see.
But looking down, even through more blue, you have a lot of light coming up from the surface, making it harder to notice that blue.
And to make it worse, you have a bunch of different colours coming up which you don't have a valid reference for to tell if it is blue or not.
You can even test this yourself (at night).
Go get 10 tiny 1 mW blue LEDs, and 90 1W warm white LEDs.
Go and place just a single blue LED pointing towards you some distance away, and see what colour you think it is.
Then go place the collection of all 100 LEDs together pointing towards you with the blue ones scattered in randomly, and make sure you are far enough back that you can't see the individual LEDs clearly, and then see what colour that appears.
The single blue LED will appear blue. Because there is no other light to wash it out.
The collection of 100 LEDs will appear white, because of the far greater intensity of light coming from the white LEDs making it so you can't notice that blue.
You can even turn off the blue LEDs and not notice any significant difference.
The fact is, we’ve seen tha at least 85% of the air is clear from planes. We’ve also seen above 30000 feet it is still blue.
Clear, not colourless. You are yet to demonstrate there is no blue below.
Conversely you have been provided videos showing it is blue below, which you then ignore.
So that does NOT prove that the air is not blue.
They had to lie about why it’s blue above Earth
No, YOU had to lie, and you continue to do so.
Again, reality makes sense and is coherent.
The sunlight goes through the atmosphere and the atmosphere scatters the light.
This explains why the majority during the day appears blue.
Importantly it also explains why the sky around the sun appears red at sunset, because the light has passed through a lot of atmosphere and has scattered away the blue light leaving the red light behind.
This also explains why a lunar eclipse is red.
It is a coherent model which makes sense.
Conversely you have no explanation for any of that.
You need magic BS to have the sky appear blue, which then magically stops working at night so you need to move things like the moon inside your magic dome, and then also make it transparent to pretend it can work, and then need entirely separate BS to explain why the sun appears red at night, and more BS for the lunar eclipse.
It is an entirely incoherent model which needs layers and layers of BS to work.