Do you believe that god reveals himself to everyone through Jesus Christ at some point in their life? Would you say that is true with the caveat that not everyone will recognize or properly interpret the nature of the revelation, but it is actually Jesus and not Allah, or Krishna or any other deity?
Understanding that Allah clearly says “I have no son” and that according to traditional Muslim teachings, Jesus was a prophet but Mohammed was the last prophet, means that there can be no reconciliation that messages from Allah to followers of Islam are actually coming from Jesus.
If you believe that god has revealed himself to everyone through Jesus Christ then we should expect to find at least some cultures who developed Christianity independently of invasion or cultural exposure to Christianity from outside sources.
Yet what we find is Christianity developed once in one place and it took a long time to spread and develop and become adopted often with changes to incorporate aspects of various cultures.
There is not one example of an indigenous society that without first being exposed to Christianity developed it independently. So clearly the belief that god reveals himself to everyone through Jesus is just not accurate.
Continuing to hold an inaccurate belief is a well understood psychological defense mechanism to avoid coming to an uncomfortable conclusion that other beliefs that rest on this one are now on even worse footing.