Cause the coil would be in the sling without it going through the bore hole. Imagine having 2 slings and the item you lift is not secured by the sling but just laying in the sling. Any movement of the slings and it will just fall out.

There probably are a lot of methods, none are as cost effective as this (as long as you secure the load properly which is the drivers primary job).

The amount of coils transport safely each year like this is in the millions, do you really think thousands of companies should invest in a lot of extra equipment due to some lazy or incompetent truck drivers not securing their load?

What do you think a magnet crane is? Sure as hell not mechanical.

Aluminium coils are a lot lighter than steel coils.

Why do you think an industry of 150 years old chooses this method of transportation?