That's literally the whole point of the WHO. Leaving it would mean either a) starting a "new" version and asking all the same people to join it (which seems to

That's literally the whole point of the WHO. Leaving it would mean either a) starting a "new" version and asking all the same people to join it (which seems to be what you're suggesting; what purpose would that serve?) or b) having no forum at all for global coordination over health crises.