It seems like a big difference but it occurred very early on in the evolution of life, so it's a disadvantage shared by all animals.

How about another example: mammalian females giving birth through their pelvises. This caused the deaths of countless women and children throughout human history. It's not as much of a problem for other mammals but it's a huge problem for humans. We've had to advance modern medicine to the point where we can safely perform major surgery (caesarian section) in order to mitigate it.

The book Sapiens has a few pages on this. Essentially, the thought seems to be that we're an edge case that's been able to jointly optimize for intellect/large brains and small efficient bodies by overcoming the limits on brain size imposed by vaginal birth. This in part explains our relative immaturity at birth. We're vulnerable and require constant care for the first few years of life. Compare this with other mammals such as calves which are able to walk roughly at birth.

> It seems like a big difference but it occurred very early on in the evolution of life, so it's a disadvantage shared by all animals.

It's possible that you could have sleepless neurons. But they would be so different than neurons we are stuck with that we might need to wait few billion years for them to show up.