Why birds do not fall while sleeping

This article doesn't even try to address what I feel is the deeper and more interesting question (but probably one that can't be answered): Why is it that horses, cows, giraffes and birds have all had to come up with a purely passive solution of "locking" themselves in place, either via their joints (for the four-legged), or via the tendon mechanism described here for birds?

I.e. why wasn't in simpler in evolutionary terms to come up with some mechanism where 1% of the brain was dedicated to the relatively simple task of "station keeping", while the rest of the brain could benefit from sleep?

Also, why didn't any animal evolve a way to avoid sleep completely?

We don't know exactly why nature can't do otherwise, but any complex brain has to sleep.

Some animals, mainly sharks which can't stop or they would be asphyxied, deal with that by having kind of 2 brains which are never both sleeping at the same time.