An attitude based on unfounded snobbery
Nearly every one of these nutjobs and cranks subscribe to the same flawed story. "Those ignorant ancients were so much less capable than us smug modern types, and we don't know how to do that. They lacked modern tools and machinery we've become totally dependent on and can't imagine not using. So those ignorant savages couldn't have done it themselves with stupid hand tools! It had to be someone else!"
We don't know how to move pyramid stones by hand because we're dependent on heavy machinery, not because it can't be done. A local 1920's movie palace has awesome faux woodwork beams (fire codes) and the method for those has already been lost! Small wonder we forget after millennia.The ancients' knowledge of hand tools, stoneworking, and architecture were in many ways superior to ours. It was all they had, so they developed it to the fullest capability. Roman concrete structures are still in use, but Hitler's giant Flak Towers are already crumbling.
The We're So Modern snobbery is misplaced, the ancients were masters of their arts. The Pyramids, Colosseum, Tenochtitlan, and others are still here, after centuries of earthquakes and vandalism. How many "modern" constructions will survive 3000 years of natural and human assaults?