If you go to see them in person it becomes clear why. The jungle foliage in this region is so thick that you could be standing 2 feet away from an ancient pyramid and not even realize that’s what you’re looking at. Besides that the area is very hot, difficult to navigate, and not particularly safe (full of narcos and rebel groups)

true, I wonder we can continue improved use of 3d mapping and lidar technologies like in recent national geographic shows.

We do, but that still doesn't change the reality on the ground. The jungle is a pretty brutal and disorienting place. I've done a few walks in the jungle in Colombia and Panama and it is incredibly beautiful but you also quickly realize that without a guide you are going to be lost in 30 seconds. Foliage so dense you can't see more than a few meters ahead and behind of you, dense enough to obscure the sun to the point that you can no longer navigate, and sometimes dense enough to interfere with GPS unless you plan on staying in the same spot for a long time. It is also incredibly alive for want of a better word.

Specifically, there are huge areas only accessible on foot or by helicopter. And good luck getting cell service. This means any injury you get can be life threatening since it may take days to get back to any kind of road.

"full of narcos and rebel groups"

This area is 60km into Balamkú ecological reserve. Are you familiar with that area? This state (Campeche) if famous for being one of the safest areas in Mexico. No, there are no narcos or rebels in these jungles. You would have to travel several hundreds of kilometers north in order to find any danger related to narcos. Everything else you said is true: Thick jungle, hot and difficult to navigate, but humans are the least dangerous things in that area.

Agreed. That area of the Yucatan is not exciting to drug cartels specifically because of its inaccessibility. By far the biggest risk is from disease which can be deadly due to the difficulty of getting back out of the jungle.

I’m referring to the Mayan civilization at large, which extends through Guatemala and Honduras. Which is certainly not safe by any first world standards (but also not as dangerous as one might think)

But “the area” in question is not that. Mexico, Guatemala, and Honduras have serious challenges but you do those and the reader no favor by conflating them.

You’re being pedantic, the original comment referred to Mayan cities, not Mayan cities in Campeche

Are you suggesting there are undiscovered Mayan cities in the heavily trafficked areas of Honduras and El Salvador?

I went to Chichen Itza last year and went to a cenote. It felt incredibly safe the entire time. It was a fantastic experience.

Yucatan state is quite safe, it’s one of the few in Mexico without a US travel advisory. It’s also got to be the #1 attraction in the state and a major source of revenue judging by how much they charge to get in

Campeche also contains some of the most interesting ruins in Mexico, like Calakmul (close to this area in question, think) and a bunch of smaller sites.

There was a good book about a recent discovery a few years ago, Lost City of the Monkey God. The locals had stories about some city in the jungle. The team managed to find it with LIDAR, but it was a slow, difficult process. They then had to land in fairly distant clearing and hike to the location. From there the team had trouble finding ruins even when they had their exact location, even once standing in right the middle of the city. The jungle hides a lot. The team members also came down with cutaneous leishmaniasis. Finding locations might be getting easier, but I imagine it would be difficult to find people with the right combination of skill and willingness to die a slow, agonizing, and disfiguring death to actually excavate some of them.

That's a better plot than the latest Indiana Jones flick.

The movies have taught me to never go on a quest to find the Holy Grail.

"couldnt someone just attach a gpr system to a plane?"

That's exactly what's driving a lot of new archaeological scholarship in jungle areas. It's not as simple as "just" though, it takes money and time and effort.

and don't forget local buy-in. can't just drop down on a plane on people and start hacking away their forest (anymore)

Nature takes over really fast.

I went on a tour of the Chernobyl exclusion zone before the war. There are parts where the bus drives through a rough path, barely squeezing through the tree branches on both sides. It looks very much like driving through an abandoned road through a forest.

And then once in a while you see a house in ruins through the window. It actually used to be a road going through a town, but it's been swallowed up to the point that it doesn't even look like one anymore. The city is of course very recognizable still, but there were plenty smaller villages.

And it's only been 37 years since then.