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?

Evolution is like DFS depth first search, it isnt looking for an optimal way optimally its just going down a branch until it finds a satisfactory solution.

Sleep according to sleep scientist matthew walker, isnt what it seems. If i remember correctly theres even more brain activity and it serves certain goals like behavior refinement, among other things not just refreshing yourself. There might not be more benefit by more sleep.