Now if you look at how larger stars operate (the CNO cycle [1]) you’ll see that it matches up with the higher relative abundance of carbon, nitrogen, and oxygen in the universe. Lithium, beryllium, and boron get “skipped over” in a sense.
Furthermore, if you look at a graph of the relative abundance of all elements, you’ll note that odd-numbered elements are less abundant than even (with the exceptions of hydrogen and beryllium). This is called the Oddo-Harkins rule [2] and it may also be playing a role.
Edit: I should also add that the third major process in stars, triple-α [3], involves the fusion of three helium-4 nuclei into one carbon-12 nucleus. This occurs in older stars that have exhausted most of their hydrogen fuel and so have built up a large core of “inert” helium. When their outward pressure from hydrogen fusion is no longer high enough to withstand gravity, they reach the much higher pressures and temperatures needed for triple-α fusion. Unfortunately for the lithium industry, there’s no chance of producing lithium this way since it is skipped over on the way to carbon.
[1] https://en.wikipedia.org/wiki/CNO_cycle
