There's that but that reasoning is more for the main characters, Bramon is only one man and each serum is expensive and time consuming, it needs to be tailor made for the individual, given his view of things, I think he is perfectly willing to hand them out like candy if he had the means and was allowed too, willing to sacrifice some level 1's for a level 2.
Ella said herself that very few Superhumans can reach level 3, let alone level 4 or 5, so most Superhumans simply aren't worth the investment. The MC and his allies are a cut above the rest, most Superhumans are the background characters that Alice was trashing for the Aldians, Michael and Tiffany even with her connections, wouldn't have been granted the serum unless they where the extreme stand outs they are.