It may not, if any such system is very energetically taxing, or would confer a host of other issues. Such a system would, downsides taken into account, have to confer a net advantage. It may be that sleep in some form is best system with the fewest downsides.

The downsides of sleep are more severe for aquatic air-breathers, and, as some other comments have already pointed out, it appears to have already been eliminated in that case.

It’s not eliminated, it’s bicameral. Dolphins do sleep, they just do so one half of their brain at a time, which is... so cool.

This is only true if you redefine "sleep" in a certain technical way. This redefinition is supported by phenomena such as the dolphin closing one eye during that eye's half-sleep cycle, but it is not obviously appropriate in all contexts.

In addition to higher energy requirements, anabolism can increase the probability of tumours. Additionally, metabolism creates mutagenic oxygen compounds. It may be that separating metabolic and anabolic states in time (wake and sleep) allows these nasties to be cleaned away before the risky business of cellular division takes place.

I guess this is related somewhat to USWS https://en.m.wikipedia.org/wiki/Unihemispheric_slow-wave_sle...

That would take extra calories, that's where the balance is

Too bad I can’t spend my calorie surplus on the no sleep extra healing evolution upgrade.