What do you mean added for non customers? The entire purpose of not adding RCS or supporting iMessage for Android devices is to create a worse experience for their customers if they interact with non-customers. Sure it likely drew more people to buy iPhones, but it's also arguably pretty awful for any society that plays apple's game rather than just downloading a cross platform app.
The tenets are in order of impact from greatest to least. They could have reduced by not making this.