This is common in specifications and standards, ISO standards are expensive to get, and good luck if you try to get the HDMI 2.1 specification. Usually, people

This is common in specifications and standards, ISO standards are expensive to get, and good luck if you try to get the HDMI 2.1 specification. Usually, people need that type of documentation if they are developing products they will later sell (although there are other uses, like hobby and research...). Not saying that I second putting such documentation behind paywalls, but it is at least in part understandable. On the other hand, paywalling documentation about a product I have anyway to pay for if I want to use it feels very greedy.