Keep in mind the only reason we see these buildings is because they are still around. They were found to be "beautiful" and didn't collapse over time. For every one of these examples there is 1000+ failures that are erased forever.

So you do have a self selection bias. Add to that weathering (things round over time), compression (things like rocks can mold into a shape over time) and just plain luck and you have the ancient aliens stuff.

Imagine what will survive from our culture for 10,000 years. Stainless steel butt plugs and dildos. Maybe they will think they are god-images.

Maybe they are.