In Afghanistan today you have an ethnic group called Moghols who speak a Mongolic language and are genetically Mongolian. They're mostly holdovers from the Mongol conquest in 1221 but are mixed heavily with Persians and only number around 2,000. Hazara's are claimed to be descendants of Mongols but are in reality Turkics from the Timurid conquest in the 15th century who were later Persianised.
Compare that to the Spanish Reconquista where Spain was mostly under Muslim rule for 700 years starting in 711 to 1492. After its completion there were zero foreign holdouts in Spain, the Berbers, Arabs and their African slaves were completely removed and made no measurable impact on the genetic makeup of Spaniards or Portuguese. There were never any communities that managed to remain. Why?