The curse may have caused the different lands to meld together though. That’s why we saw Mulan, for example, along with Prince Phillip and Aurora. They’re from different lands. Wonderland could have become destroyed, and the only remanent is a combo of all the different lands fused together. The reason Cora is a prisoner in this remanent is because she is the QoH and a threat.
But how would Mulan and Prince Phillip even know that Cora was a threat at all? Cora presumably wasn’t all that well-known way back when, and if Charming didn’t know of Wonderland, how would Mulan and Phillip?
Or she could have done something else after the possible land-melding to be thrown into the pit.