They could have created their complete custom, closed source, commercially licensed slicer. They didn't. It was probably a lot cheaper to take some else's work and slap your customizations on it.
On open source license if first and foremost the original author's decision on what can and can not, must or must not be done with their code. therefore shaming someone for ignoring the wishes is not just a last resort, but a valid strategy. Especially if it is company that wants and has money.
We wouldn't need any legal avenue when saying "don't be a dick" would work. Not respecting someone's work and wishes seems to be a pretty universal dick move from what I understand.