I'm somewhat surprised that you can't click on the person who wrote a post to see their profile. The only way you can is if that particular post was liked by someone, then the names in the sentence "This post by Fred was liked by Joe" are hyperlinks.

There's a "Profile" and "PM" button just under the signature of each post

Fair enough. That works. I'd still argue that a hyperlink is much more intuitive for the particular desire to see more about the poster, but probably not worth the effort of changing it. And you'd still need buttons for other activities like PM'ing.