[cen199]

I don't think that it is USA export restriction, because Mach3 is also a USA software and can run 6 axis and is sold worldwide.

Mach3 is taking their chances, probably because they don't want to spend months wading through the ridiculous pile of regulations.
If you want to know, you can start researching EAR part 774. You will likely have to go through several related documents before making any sense of it.
https://www.bis.doc.gov/index.php/re...egulations-ear