The puzzle here is that astronomers have no clear picture of how these ultra massive black holes are formed so early in the evolution of the universe. if you wait long enough galactic black holes can eat stars, gas, and other black holes, but there was no time for that early on. It is conjectured there were huge ‘Population III’ stars that grew rapidly because radiation transport was different when there were tiny amounts of elements heavier than helium (‘metals’ in astronomer lingo.)

Pop III stars are a bit less mysterious than dark matter but they could have played important roles in the early universe.