Why can't non-Muslims enter Mecca?

Islamic Sharia has profound wisdom in its rulings. The permissibility for a Muslim man to marry a woman from the People of the Book (Kitabiyyah) and not other disbelieving women is due to the fact that the origin of their religion is from Allah, and there is hope that she will embrace Islam. This is because she believes in the scriptures and prophets generally, so if she is alerted to the truth, she will realize it, and the husband will invite her to Islam. As for the prohibition of a Muslim woman marrying a disbeliever, it is because men are in charge (Qawamah), and a woman often follows her husband's religion. Furthermore, since the People of the Book do not believe in our Prophet Muhammad, peace be upon him, there is fear for the Muslim woman that her religion might change or that she might hear what offends her regarding her Prophet.

In another context, jurists have agreed on the prohibition of disbelievers residing and staying in the Sacred Mosque (Haram al-Makki). They differed on the permissibility of their transient passage. The Shafi'is and Hanbalis prohibited it, while the Hanafis permitted it through a treaty or permission for the People of the Dhimma. This prohibition is an act of glorifying the place and dedicating it with rulings that show its distinction and purity, so only those who are pure from polytheism and atheism may enter it.