One reason I’d imagine that with the drum machine if the top final limit failed, the cab would be pulled up into the overhead without a means to stop ending in a possible free fall of the cab and ultimately a rewinding of the counterweight back up. Sounds like a bad call back huh?
Single or double roped cabs and counterweights dead ended on the drum had to give way to the more modern traction machine as technologies were developed. Why they’re still legal is a good question. You’d think they would have gone the way of the belt driven vertical man lift a long time ago.

Thank you - now I can see why !!

Another problem with drum machines is that the cable tends to twist with every revolution of the drum. This constant twisting back and forth will weaken the cable at the shackle end and eventually cause a failure of the cable. That is why you are required to re-shackle every two years.