The default UI is how most new users will experience interacting with lemmy instances at first. So it’s helpful to create a better first impression. To the extent that this is built into the project itself makes it easier for other UIs to be created and maintained too.

I believe that the Lemmy devs are working on a better url scheme for posts and comments as well. This will also make it less annoying without any browser extension, script, or other third part service.