> Other end-to-end open-source systems are more widely used like Signal are the same, not exactly easy to insert a backdoor into a system that is a) open and b) completely distributed with no central key authority.

If Signal weren't available from any of the major app stores, such that it didn't work on iOS at all and didn't work on Android devices without turning on the intimidating option to allow non-Play-Store apps, how much usage do you think it would get compared to today?

Making real security hard to get would cause far fewer people to actually use it.