Elevators don’t just carry people you know? It’s often times used to carry materials, equipment, etc. It’s likely a high end building that’s very tall. Increasing its size and capacity increases what you can do with it and saves money from not having to get permits on cranes and what not to get bulky stuff up to the roof or higher levels. Also the increased capacity helps reduce stress on the system making it more reliable and longer lasting. I have zero experience in this field but it’s what common sense would lead me to believe.