Your idea that people will necessarily buy things if they can't get them for free is nonsense, as is the likewise idea that people don't and won't buy things from creators they can get for free.

I’m just going off of what I’ve been told directly from the artists in question.

Sometimes if you Google these artists’ names, the majority of the results are bootleg scans. They have no way of combating that. 

Gengoroh Tagame explained that when an Italian publisher was interested in publishing a translation, they told him they didn’t want any existing work because it’s all already available online.  So he would have had to create an original work entirely on spec, which is pretty much impossible because then he wouldn’t be able to meet his deadlines for the manga magazines that employ him. 

We’ve helped him and other artists put out plenty of books that are already online for free, and you’re right, people still bought them– sometimes even if they’d seen the scans. But I’ve also been at plenty of sales events where people come up to the table, pick up a book, and say “I’ve already read this one online” and then don’t buy it.

Supply and demand, it’s real!