There's this gravely mistaken idea that a business's interests are fundamentally based on serving customers' interests. But both sides of any transaction have diverging interests, and in the real world we see industries uniformly implement arbitrary customer-hostile practices rather than compete. This is especially true when the customers' downsides are not easily quantifiable - see the entire advertising-surveillance industry.
And sure, there is always some prudent-sounding reason why more centralization is needed (essentially the "God narrative"), which is exactly why the safety-above-all ratchet moves ever forward. But in the free world this type of thinking is a red herring - the same scare-reasoning can be applied to mandating that every person have a machine-readable ID code tattooed on their forehead, and this only seems unreasonable because it's not present custom.
If a forum had the option of requiring real-world ID, they'd make the reasoned business-case tradeoff of whether that's likely to improve the forum/business (less trolling) or worsen it (far less signups because people want to be anonymous on that particular forum).
And as for hotels specifically, they require a real identity for public safety, so police can (not just at check-in, but even months or years later) determine where someone stayed in order to solve cases of murder, child trafficking, or other violent crime.