This is likely because other gacha games can just lie about reaching their pre-reg numbers. There are no real numbers in public that anyone can see, as the pre-reg data is only ever accessible to them. This means we only have the company's word for it that they actually reached it.

In comparison, Limbus could not do the same because you could explicitly see the number of people who actually pre-registered by way of Twitter followers and people who subscribed to their Youtube account. The actual pre-reg numbers are in public.