Why can posts not be links/URLs? Isn't that a pretty huge part of reddit posts? When submitting a post, why do I need to come up with a URL like non.io/example

Why can posts not be links/URLs? Isn't that a pretty huge part of reddit posts? When submitting a post, why do I need to come up with a URL like non.io/example-i-made-up? If I leave that blank I would expect it to just assign a random or UUID URL.