20 years ago when the CAD business was very different, many CAD software
companies spent huge amounts on various trade shows. Of course the market
was different and a CAD system often meant a million dollar investment for
just a few seats.
The International Machine Tool Show used to be an important show however
since CAD software has become virtually a commodity many companies have
concluded that the expense of doing a show targeted at this narrow niche
doesn't make sense.
I don't know the specific reasons why Autodesk selects one industrial show
over another however quite a large percentage of attendees at this show are
often looking for the latest in carbide inserts or water jet CNC and not
specifically for CAD software.