Because you fucks seem to not know what an average Joe means. You guys think just because Clark is humble and wants to be human a lot that this means he's just like you and me when he isn't. Specially when DC won't stop reminding us all the ways Superman is better than... pretty much anyone or anything. It doesn't work like that.
Spider-Man works as an average Joe kind guy because the comics constantly push him around and we constantly see him down on his luck. Not to mention that he's constantly dealing with mundane shit that everyone one of us have to deal with. But even then is kinda of a wish-washy situation because the moment writers start to throw hot babes at him or reminding us over and over that Peter is a genius the whole "average Joe" fantasy jumps out of the window. But at least i can give Marvel the benefit of trying.
DC never tries to really explore the myriad of ways Superman can be like one of us dealing with shit we all deal and having our shitty luck. We rarely, if ever see any of that. Instead what we see is a lot of meaningless character wank with everyone Superman interacts with blowing smoke up his ass. Everyone loves him, everyone wants to be him, everyone wants to fuck him, everyone needs him, and the only people that hate him are villains who are just mad jelly they aren't Superman. He has a fortress filled with cool shit that is pretty and he has friends in the far future where he's even more beloved than in the present. But hey, Superman is an average Joe too! Because... because... well, because... he's like really, REALLY humble like Jesus Christ was. Maybe even more, because he's nicer and more special than Jesus Christ.
Can you see how that shit doesn't work?
DC should decide if Superman is the very best of the best... oooor if he's an average bloke with average problems that makes his life hell. It's literally one or the other.