There’s nothing to stop other people posting up rides. That would be a good thing.
For me, personally, I need the peace of mind that I’m insured as ride leader. To get that it’s easiest if my rides come under the auspices of a club such as The Fridays which has a strong alignment in approach with my themed Sunday London rides. Both are accessible to all, conversational paced, social affairs.
£2 a year and insurance cover (which I should have thought is desirable anyway, and can be had for a discount on payment of the £2 membership) doesn’t seem too much to ask. Especially as the rides themselves are free.