Actually, it often is - using non-oem parts can invalidate certifications, particularly in safety-critical functions. Never mind that though, who wants to get into a lift that’s had parts made up by a non-specialist firm and what kind of firm would take that job on?!
It's not a question of replicating a part, it's a question of would the insurance company allow that part to be used on the lift.
And they won't.