Since the pandemic started and all conferences moved online, the GNOME ones are the only one I’ve seen that require people to register in order to access talks. Privacy conscious friends have told me they would not attend the events because of that, and I can’t think of a good reason to actually require registration. Unlike for physical events, counting attendees is easy, as BBB (used for streaming talks live) and Youtube (used for publishing talks after the fact) give you the number of participants or viewers. In fact, given we publish talks afterwards, friends have argued that incentivises them even more not to participate during the event and they’d rather just wait for the talks to be made available.
GNOME often stated that it cares about privacy, so it should show it and aim at collecting as little data as necessary.