How did the Earth end up with 78% nitrogen in its atmosphere when no other planet has more than 5%.?

Our planet was primarily composed of Nitrogen a few billion years ago part of this was due to outgassing. When stramatolites a small organism began to form near shallow waters, were one of the beginning stages of photosynthesis; the process in which light is absorbed like plants do and turn the co2 into oxygen through a specific process. O2 formation created the ozone layer through a process called photolysis or photo dissociation hence blocking out some harmful uv light towards the earth allowing plants and other creature to thrive on the earths surface rather than just water making a safer environment.

This created even more oxygen due to more vegetation and so i believe the oxygen was balanced out the excessive nitrogen. Keep in mind that too much oxygen is no good for us, the nitrogen we breath ~78% dilutes the ~21% where your body uses the oxygen and expels the nitrogen as its not much use through respiration but the nitrogen u get from food is useful.

So thats how earth pretty much got its nitrogen and then oxygen but i don't know why we have more than other than the fact that a lot of it was produced from outgassing each planet is different just like we are all different but i really don't know. Just because we need water and oxygen to survive does not mean other living creatures like micro organisms need the same like us in fact bacteria that are here on us now can survive in space so that means that it doesn't necessarily mean that all other planets need the same criteria that our planet has to create life. But other planets not in our solar system can have nitrogen.

Also that mass like the other guy said is a good point as well.

That is the curious part. In the process of planet formation the accretion disc wasn't homogenous but substances gravitated towards Sun were more dense and less gaseous. May be, Nitrogen found its right depth at the spot where Earth is now. In the outer gaseous planets free Nitrogen is rare but is compounded in the form of Ammonia (a Hydride) & Oxides. One reason for Ammonia formation there could be the excessive "Lightning" activity in the atmospheres there, similar to Ammonia formation on Earth.

However, in my opinion, this too was one of the contributing factors towards the formation of Life as 18 Amino acids are required for higher forms of Life. Amide radical of these acids has Nitrogen as the basic atom in it.

Given the huge mass of the atmosphere of Venus, it is very possible that the 3.5% of N2 in it is actually more than that of Earth. Not knowing the mass of either atmosphere does not allow me to calculate the actual quantity, and it is not stated whether the 3.5% is by mass or by volume.

Aside from that, the gas giants probably have far more nitrogen than the Earth