Explained: Ant-Man, Variants?

In the Quantumania Trailer, various Ant-Men are running towards a nexus fleshy heart, but how do these variants exist and who are they? Explained!

Scott Lang first comes across one of his variants when he first enters the nexus heart, thing, so it has something to do with that, but what, and why can't Kang do it?

There are two explanations for this, in Ant-Man and the Wasp (2018) when Hank first landed in the Quantum realm, echoes of himself filed around him:

Now Scott is closer to the supposed, Heart of the Quantum Realm, so the echoes are much more vibrant and vivid, that they seem like real people. I think some of the first few echoes of Scott will start running towards the heart, so much more echoes would appear because they are closer to the Quantum Heart.

His echoes will guide him to here he has to go, and since Scott works with other people well, this would be no problem for him, but with Kang, we know from Loki (2021) that Kang variants don't work very well together.