At an organizational level, you are correct. There are very few places left unexplored by the human race on this planet. However, on an individual level, if you have never been to the summit of Everest, then it is very much a personal exploration. Maps and guides reduce the required effort from superhuman to formidable, but I see a clear exploratory factor.

At a personal level -- answering the question "what have I explored" rather than "what has the human race explored" -- the chasm between having crossed the Hillary Step and merely having read a description of it is vast. You are exploring your own limits in a purely figurative sense, and this could be boiled down to "thrill-seeking", but you are also literally exploring the terrain and geography, figuring out how to hoist your own personal mass beyond each obstacle. It is this very personal sense of exploration that I think drives most non-professional mountaineers.

Also, even at a macro / organizational level, completely new routes are tried (explored!), and the route through the Khumbu Icefall changes every year.