This doesn't seem to have been firmly established, but as far as I can tell it's currently thought to be related to how carbon in the solar system's protoplanetary disk behaved when it was vaporized after fusion began in the sun. The question was studied in this paper published in 2021 [1], which is discussed in this article [2].
The authors of the paper suggest that the material that formed the Earth was depleted of carbon early in the solar system's history due to solar activity, and that most of the carbon now on Earth was delivered to the planet later on directly from the interstellar medium.
I should note a couple of clarifications to my first comment: the elemental abundance I mentioned for the universe and Earth's solar system does not include helium and neon, which are abundant, but are usually ignored in this context as they're noble gases.
There is also estimated to be slightly more mass in the present-day universe in the form of iron than nitrogen due to the high mass of iron atoms (nitrogen is the fourth most abundant element by mass in the human body, but the body contains relatively little iron). The number of nitrogen atoms in the universe, however, is substantially higher than the number of iron atoms. The amount of iron in the early universe should also have been lower; the element is formed late in the stellar life cycle [3], whereas the other cosmologically abundant elements that are relevant to biology (carbon, nitrogen and oxygen) are formed earlier [4].
The authors of the paper suggest that the material that formed the Earth was depleted of carbon early in the solar system's history due to solar activity, and that most of the carbon now on Earth was delivered to the planet later on directly from the interstellar medium.
I should note a couple of clarifications to my first comment: the elemental abundance I mentioned for the universe and Earth's solar system does not include helium and neon, which are abundant, but are usually ignored in this context as they're noble gases.
There is also estimated to be slightly more mass in the present-day universe in the form of iron than nitrogen due to the high mass of iron atoms (nitrogen is the fourth most abundant element by mass in the human body, but the body contains relatively little iron). The number of nitrogen atoms in the universe, however, is substantially higher than the number of iron atoms. The amount of iron in the early universe should also have been lower; the element is formed late in the stellar life cycle [3], whereas the other cosmologically abundant elements that are relevant to biology (carbon, nitrogen and oxygen) are formed earlier [4].
[1] https://arxiv.org/abs/2104.02702
[2] https://phys.org/news/2021-04-stardust-pale-blue-dot-carbon....
[3] https://en.wikipedia.org/wiki/Iron#Cosmogenesis
[4] https://en.wikipedia.org/wiki/CNO_cycle