And without the main festival, the fringe events would not take place.
Each post Christmas period see numerous folkies gather in Whitby for a whole series of mainly spontaneous events

The situation in Edinburgh is that the "official" Festival is now more dependent on the Fringe than the other way round - the Fringe became far larger very early on, it's what brings most of the audience into the city, and it's more likely that people will buy "official" festival tickets as an add-on to their Fringe spending than the other way round.

Something I hadn't realized until it was recently pointed out in an FB post: WFW doesn't pay pubs where they run workshops, even when they run them in such a way as to preclude any significant bar sales (which happens fairly often with workshop events). This isn't pointed out to any of the participants, so they don't necessarily feel any obligation to spend anything there. Contrast the situation with sessions: it is always pointed out at any Eurosession that the venue needs our custom, and in the Irish session scene nobody is ever going to need reminding of that. So if you're a publican, which would you rather have using your space?

WFW shrinks slowly year on year. The fringe isn't expanding fast enough to compensate (the Eurosessions and the Irish sessions are significant but static), and it would be to the great benefit of local venues if it grew. One potential that comes to mind is more open-mike events; not really my thing but they would attract people who aren't very interested in official-WFW.