Why doesn't every android phone come with a built in video calling app??

I'm assuming every android phone uses google playstore. Why don't phone companies and google just work together and make a video calling app specifically designed to be used for video calling. An app that comes preinstalled in every android phone by Google so all android users regardless of what brand of phone they have can video call each other using their phone numbers. It doesn't matter where you are in the world. As long as you have a phone number and internet, you can video call whoever want. 1 app. For all androids. By Google.