Exactly, several apps don't offer that. I'm asking to force developers to do that, because their in-app browser do not support content blockers or saved logins and at most have a button to reopen the same page in Safari - which I do 100% of the times. This is a waste of time and bandwidth, not to mention when I found myself subscribed to a stupid ringtones service.
Some apps are even weirder. Gmail the first time asks you which browser you want to use: Chrome (suggested, of course), Safari, or the internal one. But if you choose Safari, it uses the internal one anyway, there's jsut a button to reopen the same page in "external" Safari, and after some time it asks again (just in case yuou changed your mind...). Instead, if you choose Chrome, it opens Chrome right away and never asks again.