Kaaba is the holy place for muslims becoz muslims worship here and the place of worship is always important and holy not even for Muslims this is the custom of every religion you can see more on Respect of Ka'aba. read more
Allah says in Holy Quran: "Mosques are house of Allah" and so we have special care and respect for Mosques. When talking about Kaba, it was the first build Mosque that was build by Adam(A.S) and Allah has also said more about Kaba so it is important for Muslims. read more