There is no fundamental reason why native apps can not expose shareable links just like any other. And on the other hand with the prevalence of single page webapps etc its far from guaranteed that you can get usable links from webapps.
A web link is easily shareable on the assumption that anyone you send it to has a web browser. A link to a native app requires you to assume that the recipient has the app installed and is on a platform where app URL schemes are well-supported.
Direct linking inside apps has been enough of a pain in the mobile world that entire companies have been built around it -- and the solution that those companies tend to use is built on web links. Android and iOS have also been moving in that direction.
None of them are great. Android and very recent iOS are doing OK. Desktop OSes are still pretty bad. Clicking a non-HTTP protocol link in Chrome pops up a huge, user-unfriendly "External Protocol Request" dialog that warns of a possible attack on my system. That's pretty par for the course for desktop browsers.
