Cause that's what other artists do. If I want to have fun and listen to great music, I'll go to an Aerosmith, R.E.M., etc. concert (two of my favorite bands, by the way. I've seen them live and it's AMAZING.) But with U2, I do those things and a lot more. You feel completely different in front of that giant screen, those visuals. It's just unique. And that's why ZooTV and Popmart are the 2 best tours ever and that's why I want to see U2 pushing the limits again. (I don't want in no way Zoo, Part II!) They had their time to rest, now it's time to do something new again.
I understand your point and I agree with it...I loved Zoo TV and all of its asthetic (sp?) excesses, Popmart...well, not so much, but I appreciated the massive visual show. I loved the elevation and vertigo presentations as well, in fact elevation was my favorite tour. I have no doubt that the Horizon tour will be an extravagant and brilliant show, and I have no doubt that I will love every minute of it.
But in response to your first sentence, why can't U2 do it as well? (the simple show that is.) Where is the rule that says U2 is locked into the over-the-top craziness? What if, just what if, just for once the music spoke for itself? It comes down to taste, obviously, and I would never hint that this anything other than opinion...but you cite good examples of REM and Aerosmith. I submit another is Pearl Jam. Their last tour (2008) was mind-blowing with almost zero visuals, special effects, etc.
Obviously, some folks prefer the lavishness, some prefer the minimalist. I like both. All I'm saying is for the past four world tours, U2 has bombarded us with the most incredible displays of performance technology imaginable (elevation to a lesser extent), and done it brilliantly. What about a radically different approach now, where the music IS the special effect? At the very least, the setlists could be more dynamic and less predictable, bono's "bonoisms" would not be so tied-into whatever is on screen at the moment and would not be so scripted/forced, there could be more acoustic versions, etc.
Finally, as far as overall legacy is concerned, I think U2 has much more to gain by taking a less is more approach for the horizon tour. Twenty years from now, the technological craziness of the zoo tv, popmart, elevation, vertigo and (presumably) horizon tours might blend together in the collective memory. A completely old school, four guys playing the club kind of tour might really stand out as a gem and separate it from the others.