Why did the reconquista stop in Iberia? Arguably, the Maghreb was once a Christian land and probably still had a Christian minority at the timd. I read there were even pockets of indigenous Romance speakers until the 15thstate century.
The Reconquista did not stop, it just failed. Both the Portugese and Spanish attempted to conquer North Africa. Portugal was decisively defeated in the Battle of Alcácer Quibir in 1578. Spain was eventually defeated as well, but at times controlled or ruled multiple cities like Oran, Mers El Kébir, Algiers, and Tunis and others. Even today Spain still controls Ceuta and Melilla.
The reasons for the Iberians defeat can be classified in several categories.
1) The sea barrier aided the Spanish in regaining Iberia, and hurt them in conquering Africa. It was the exact opposite for the Muslims.
2) Spain and Portugal had other commitments and opportunities that took their focus off of controlling North Africa.
3) All of their conquests in North Africa were superficial and concentrated on the cities. They didn't seem to want the hinterlands that would have provided land and agricultural basis for settlement.
4) Too easy for their Muslim enemies to hide in the mountains to avoid them and attack Iberian ruled settlements as convenient.
5) The Ottoman threat put too much pressure on Spanish capability to control North Africa.
6) The population of North Africa was thoroughly Muslim. Christianity died early there. In contrast, Muslim Spain always had a large Christian population, and even those who converted to Islam often had Christian heritage they could fall back on once the wars went the other way. Christian Iberia had few potential collaborators in Africa.
7) For Spain, the critical time to control North Africa not only coincided with fighting the Ottomans, it also coincided with the Dutch Revolt. Their resources were too split.
If changes in the 16th Century had been different, it is possible that a permanent Christian presence in North Africa could have happened. If Portugal won Alcácer Quibir, and Spain got some breaks or didn't have to contend with rebellion in the Netherlands, or if Lepanto was followed up on better, it might have been enough for a long term Christian presence.
The odds were against it, but not so much to be implausible.