Credit arithmetic is the usual reason. The allowance is shared across eighteen tools, so the rewriting budget shrinks whenever anything else is used, and people who bought it for one job find the number moving under them.
The second is the unstated per-request cap. Monthly credits are published and the longest single passage is not, which matters on long documents.
The third is scope. It is a content-production bundle, so there is nothing in it about disclosure, institutional policy, or what to do if the authorship of your work is questioned.
None of that makes Netus AI a bad tool. It makes it a tool with a shape, and the question is whether that shape matches your work. Our full HumanFlow vs Netus AI comparison sets its numbers against ours in detail, including where Netus AI wins.