Sometimes They may, But…
The primordial black holes comprising the dark matter are not uncharged Kerr black holes. They are highly charged Kerr-Newman black holes and consequently they have strong magnetic fields too.
Do subatomic nuclei clump into supermassive nuclei? No. There is a limit to the mass of a stable nucleus. The charged nature of nuclei limits how and to what extent they can combine with other nuclei. I view the so-called “strong force” as atomic scale gravitation that is limited in range due to the fractal geometry of nature. There is a long explanation for this that is simple in terms of principles, but complicated in full detail. It is called Discrete Scale Relativity (see link below).
Both subatomic nuclei and analogous self-similar stellar-mass ultracompact objects can combine by specific rules of physics to form more massive nuclei up to roughly plutonium-mass, and black holes up to about 36 solar mass, respectively. DSR is consistent with the scaling for these analogous mass limits.
In very extreme environments and very energetic conditions, like the early phase of the Big Bang, EM forces can be overcome and supermassive objects can be formed. In fact one of the leading explanations for how supermassive black holes appear to be formed in the early universe, involves gravitational clumping of stellar-mass PBHs. But we are still far from accurate and detailed models of those processes.
Thanks for the question.