Why didn't the scientists in Stranger Things recognise this place?

Why should they?

1. First, why would they mark the location? To them, there’s nothing special about the location. It’s just where Hopper happened be. If they’d had no map of the area, maybe they’d have marked it to try to guess where the tentacles were—but they have a perfect map, thanks to the photos they took of Will’s drawings. No need to guess where the tunnels are relative to their lab, because they have all the information. And indeed, that’s what they’re going off of, if we look at what’s laid out on the table.

   

   

2. And all this is happening over the course of what, a week? I think it may even be a day or two since they found Hopper. I’m not terribly surprised that they wouldn’t have seen the need to mark the place where Hopper was, or frankly even had time. It takes a while to put together a good map. And this isn’t the age of Google Maps or anything. There’s one map, and it’s in that room.

3. And even if they knew where Hopper was above ground, and had decided to record that for some reason, so what? They know where he is relative to their lab and other above-ground objects, not relative to the underground maze of tunnels, which they’re navigating based on Will’s map. Given how tangled the map is, the only one who’d remember where he was relative to the tentacle map would likely be, well…Will.

4. Are they really so methodical? Humans miss things. That’s just how we are. They missed something pretty big—that the Mind Flayer was spreading its tentacles into Hawkins below the Gate. It’s understandable, of course—the mind flayer was playing things safe, making it look like they could burn it back, while it was stealthy as could be underground—but it’s a big thing to miss. They can miss marking a spot on a map, even if that would be the absolute most careful thing to do.

5. Finally, what was there to notice? Even Hopper didn’t realize what was going on, precisely, until Mike told him it was a trap. He was suspicious that it was where he had been before, but it wasn’t like he suddenly realized what was wrong. Even if the scientists had known that this was in the area Hopper had been in before, I doubt they’d have thought anything of it. Why couldn’t there have been something there that the Mind Flayer didn’t want them to see?

The bottom line: It’s obvious to the viewers, who haven’t had to remember various little details of an amorphous map in a high-stress situation, where Hopper’s location is relative to the map below ground, and the map above ground, and that it’s something worth remembering.

Unfortunately, within the show, the only one with all this knowledge is Will—and even more unfortunately, the Mind Flayer had him then.