I have heard others mention this happening as well. I have only seen baby worms on my lid once, and that was on the rare occasion that I checked the bin after dark. More frequently I have found adult worms on the lid. Maybe it's what all the cool young worms are doing in your bin.

My guess is baby worms have smaller mouths and eat smaller things that may be on the cover. Maybe baby worms have more wanderlust than adults.

Back when I had my bin in the basement, I would find worms on the roof of the bin all the time. Now that I moved and don't have a basement, I hardly ever find them on the roof. The basement was always kinda cold. Worms are cold blooded. Maybe they climb up to get warm? Would that make sense? The air should be at least a little warmer at the top of the bin, unless there is hot composting going on in the muck.

I also find tiny red worms on the lid at different times and sometimes they move off the lid and other times they get stuck and die right on the spot . I too find this behavior curious

I no longer see baby worms on the lid since I started leaving the lid cracked also my plastic bin no longer sweats because of this. The gap can be varied as needed.