it is mostly fire code and other such things. five stories is about the maximum amount of traditional (not-CLT) wood construction tolerated by fire code. also,

it is mostly fire code and other such things. five stories is about the maximum amount of traditional (not-CLT) wood construction tolerated by fire code. also, six and above stories is where you start needing more elevators as a practical matter, which cuts the amount of leasable space on lower floors. if you look at skyscraper designs one of the most complicated things is elevator layout design, because you need enough capacity so that people don't wait unreasonably long for elevators, but you also don't want to waste so much space on elevator shafts.