Why is the early universe too bright?

 One of the things the JWST discovered was a swarm of mysterious early galaxies that were just...too...bright. They didn't have time to form enough stars.

Now we've worked it out. They aren't massive, but it turns out that in the early universe, stars may have formed more explosively, in rapid, bright bursts. As galaxies got bigger, the process (gas ejection from supernovas) became impossible.

It's kind of like a forest. Large numbers of saplings grow in a young forest but are crowded out in a mature one, resulting in steadier replacement.