I have heard of this explanation before, and I agreed at the time. But later when I found out they started nerfying coffee and jewelries, which were not cheap, and not trash, I was confused.
So I thought, let say, ANet sells research note at 50C each, then all the trash items/ wasted resources below 50C (which they often are), would still be salavaged by players that are constantly looking to beat this price bar of 50C. When the cost is above 50C, players would naturally stop. This way, players would still be researching for cheaper options, while keeping Devs' idea of resource sink.
Nerfing crafted items such as coffee really makes no sense to me. Players just have no ways of knowing the rules behind research notes. There are no indications that tell players 1 whether or not they would get research notes, 2 if yes, how many? Setting an official price for the research notes just eases Devs' workload, not having to manipulate the market by nerfing random(seemed to players) items. I just hate the ambiguity, confusion, and uncertainty behind research notes.
Best,