The Christians were greatly weakened and across the Mediterranean -- between the Umayyad conquest of Spain and the interminable Italian wars and then the Carolingian wars, there was no real way to coalesce a Western expedition to the Levant before the timeframe of the Crusades. The Romans, OTOH, were not having a good time of it themselves, with numerous hostile frontiers, iconoclasm and the Roman national sport -- civil war -- to deal with. After the fall of Jerusalem again, the Romans were still weak and the Western Europeans were drawn into their own conflicts, especially the Hundred Year's War.
Taking Mecca -- let alone defiling it -- just doesn't seem worth the cost or hassle. They are ruling over a large Muslim population -- as opposed to the early caliphs, who conquered Christians that had greater grievance with Constantinople than with the nascent Muslim faith. They are surrounded by Muslim powers -- the Almohads if they have Egypt, the Fatimids if they dont, and the eventual successor to the Seljuks in Iran. The Qarmatians, OTOH, were a Shiite religious movement drawing on existing and reinvigorated Shiite sentiments in the aftermath of the crippling Zanj rebellion and the rise of the Fatimids -- a much different playing field compared to overstretched European conquerors who rely on foreign allies to win any sustained conflict with the Ummah. That part of Arabia and Iraq had been the historical center of Shiite partisans since the time of Ali and Hussein.
The Muslim infighting helps them out, as we have seen in the 2nd Crusade -- but openly defiling Mecca will have consequences. After all, Fatimid Caliph al-Hakim's atrocities against pilgrims and the Holy Sepulchre were one of the major motivations for the Crusades IOTL and ITTL. I see no reason for Muslims to react differently, particularly when they have shorter supply lines and a ready-made fifth column throughout the Crusader state. A proper response may take decades; personally, the risk of revolt and reprisals from, say, the Hashashin, would be immediate.
And it's not as if the Romans would necessarily bail them out either, which a) deprives the Crusaders of their best ally with the best supply lines and b) makes the travel of Western European help that much harder.