Maybe "hate life" is putting it rather strongly, but look at it this way. If someone was tapped to play Superman at the same time Christopher Reeve was playing him onscreen in the 70's, wouldn't it be a wave of comparisons between the two that would overshadow the movie or show?
Stephen Amell is doing for Green Arrow, what Christopher Reeve did for Superman in the 70's, and Christian Bale recently did for Batman. End of story!
He took preparing for a role like this to the next level. Stephen Amell can actually shoot a bow & arrow, flip, kick, and punch in a disciplined manner that makes him in "real life" a tactical asset to take with you into a "real fight". The videos of his "parkour" training techniques is out there on Youtube if you think I'm wrong.
So why would anyone who makes acting their profession want to play Green Arrow on the big screen and then spend a ridiculous amount of time hearing the comparisons with Stephen Amell's version of the character playing on the CW right now? It's like sitting at a table to eat Ghost Peppers willfully knowing full well what comes next!
I recently read on Stephen Amell's Facebook page that he never had studio level discussions about playing Green Arrow alongside Henry Cavill, Batfleck, and Gal Gadowoman. It's obvious this isn't an easy collaboration to execute, but like all things it is possible.
DC , Warner Bros and the CW have a lot to gain from a partnership between the two projects. "Arrow" can successfully do for JLA what Marvel wants "Agents of Shield" to do for their projects or vice-a-versa.
So yea, anyone else playing Green Arrow on-screen at the same time Stephen Amell is bringing his "A" game on the CW would probably hate life, alongside those behind the decision in casting him as well.