Typically, when you cannot download apps, that are still compatible with your iPhone's iOS version, the issue is not with iOS (as you surmised,) but could be with the payment method you are using with your Apple ID. This would tend to affect all app downloads, not just a select few. If you are having issues downloading any app from the store, then that's where I'd start looking.
If not, then the only other thing I can think of is that these particular apps are banned from where you live. Just a wild hunch. Regardless, you can certainly wait to hear from others here or you can contact Apple Support directly by using the "Get Support" link in the upper right-hand side of this forum's web page. Good luck!