Indonesia had potential for their Islam to go to the left, but American intervention created reactionaries over there. Secondly, lots of Global South adaptations of religions are syncretic and lots of white leftists view the religious parts of the global south as equivalent to the weirdo American ones. Sure, there are reactionary elements in the religious for that part of the world, but religions like Christianity is practiced waaaayyy different from the global north. This is why you see openly queer people in churches in the Philippines, religious metalheads in Indonesia, lots of different religious practices in Chiapas, and you'll see Santa Muerte in Mexico.

Indonesia even had their own heroes who wanted Islamic communism, but western leftists did not even want that to happen because they saw Islam the way they saw the Ottoman empire.

edit: Also, there's a good number of Christian and religious people in the American left. But why would you admit that unless the conversations say so? If you hang out in social justice spaces long enough, you'll see activists who wanted to be or are part of the clerical class.