Stupid question but how were they cut originally ?
Was it done in the factory or would the bike shops have been
equipped BITD ?
Usually in the factory, with a big tool (special machine tool in the bigger factories, hand tool in smaller frame builders).
BITD a good number of shops would have also had the tool, or a cheap "non-factory" version of it) along with cutters/tools to do a good number of basic frame repairs. (Straightening and thread tapping mostly).
Since the event of the aheadset, most shops now just carry a steerer cutting guide, and a hacksaw.
And most modern frames can't be cold set easily, or at all, and retapping stripped threads in aluminium is a world of pain, and regularly unsuccessful!
So we end up with a handful of specialists, and most shops simply can't do the job.