Because of what Christ has done for us!
The area where Christ was crucified was not originally inside the walls of the Old City in Jerusalem. But as the city grew, was attacked, destroyed & rebuilt, the walls expanded. This is the Church of the Holy Sepulchre, the area identified as the site where Christ was Crucified & buried. The care of the church is handled by 6 denominations: Greek Orthodox, Armenian Apostolic, Roman Catholic , Coptic, Ethiopian and Syriac Orthodox churches.
But if you are Christian, there is only one Church, and Christ is the Head (Colossians 1:18).
We are many denominations (and non-denominations) because God expresses Himself in a myriad of glorious ways. But, we are one Body: “There are different kinds of gifts, but the same Spirit. There are different kinds of service, but the same Lord. There are different kinds of working, but the same God works all of them in all men. Now to each one the manifestation of the Spirit is given for the common good.“ 1 Corinthians 12:5-7
God Bless you all
(click an image to enlarge & start the carousel view)