Picture two buildings across the street from each other. Both have one elevator, both serve four floors, and the cabs look almost the same inside: same brushed steel walls, same row of buttons. It's natural to assume they cost about the same to keep running. Often they don't, and the reasons are mostly things you can't see from the lobby.
What's behind the walls is different. The cab is just the box people ride in. What moves it can be quite different from one building to the next. Some elevators are pushed up by a piston filled with oil (a hydraulic elevator). Others are pulled up by steel cables over a motor (a traction elevator). Each has its own wear points. A hydraulic unit needs attention to oil, seals, and the piston. A traction unit needs attention to cables, brakes, and the motor. Two cabs can look the same and sit on top of completely different machines.
Age doesn't always show. A cab can get new panels, flooring, and lighting while the equipment behind it stays decades old. A freshly updated interior can hide a controller (the elevator's "brain") that's 30 years old and getting harder to find parts for. The reverse happens too: a plain-looking cab may run on fairly new equipment.
How the elevator is used matters a lot. An elevator in a busy medical office might make several hundred trips a day. One in a small condo building might make a few dozen. Doors are usually the part that wears out first, and every trip opens and closes them. Heavy use, rolling carts, or delivery traffic all speed up that wear.
The space around it matters too. Heat, humidity, and dust affect equipment. An equipment room that gets hot in summer, a pit (the space below the lowest floor) that collects water, or a building near the coast can all shorten the life of parts that would last much longer somewhere else.
History adds up. An elevator that has had steady, regular care tends to have fewer surprises than one that went years with only emergency fixes, even if both run fine today.
The practical takeaway: when you're comparing your building to another one, or looking at maintenance prices, don't go by how the elevator looks. Ask three plain questions: What kind of elevator is it (hydraulic or traction)? How old is the controller? Roughly how many trips does it make on a busy day? Those answers say far more about what your elevator needs, and what it should cost to care for, than the cab ever will.