Granadan Muslims converted mainly because no foreign Muslim aid ever arrived

Evidence

And yet at the same time many Granadan Muslims, unable or unwilling to fight yet another war, did accept conversion. The sustained military action, the repeated evangelizing campaigns, above all, the absence of any significant aid from Muslim countries overseas, combined with the promptings of these local leaders who were collaborationists, must have convinced those who wished to stay on in their homeland that sooner or later they were going to have to accept the baptism that was being thrust upon them, and so they were perhaps well advised to do so on the best terms available. — L. P. Harvey, Muslims in Spain, 1500 to 1614, 218