Volume is the usual reason. 5,000 words a month at entry is roughly three undergraduate essays, and people writing weekly exhaust it in the first fortnight.
The plan structure puts others off: Premium at $14.99 sits one cent below Unlimited at $15.00, with Premium capped. Once you notice a decoy tier, the rest of the pricing gets harder to read at face value.
A third is the entry allowance itself. Standard carries 5,000 words a month, roughly three essays, which most weekly writers exhaust inside a fortnight. The generous 3,000-word per-request cap makes that ceiling feel closer than it looks, because a single long document can take most of a month's budget in one paste.
None of that makes HIX Bypass 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 HIX Bypass comparison sets its numbers against ours in detail, including where HIX Bypass wins.