I don’t know enough about those countries political to give like an actual analysis of the situation, but isn’t the obvious answer that countries usually don’t like having enclaves within their territory?

Spain is opposed to British control of Gibraltar in the same way, and while Britain’s claim is a bit more shaky, Spain’s history of colonizing North Africa is going to make the existence of their enclaves in that territory an even more thorny issue than it already is.

Old colonialism is still colonialism

The militarized borders aren’t exactly neighborly. In fact, they seem to perfectly highlight the global north/south divide.

It feels to me like Spain has a better claim on Ceuta and Mellila than Britain does on Gibralter, and the Falklands, and Than Morocco does on Western Sahara

Not true since all they both have zero claim on all of those 😏