Because right now, the CA/B Forum believes that they cannot just completely blow off the concerns of orgs that are having problems adapting to the new requirements because they have legacy tech investments that use the Web PKI for purposes it's not a good fit for. This causes them to move more slowly than the less conservative stakeholders would like. If those concerns were lessened, then the CA/B Forum would feel freer to move faster.
I don't see a reason why that should be a problem to solve for public CAs and rest of the internet? Complaining about multi-perspective validation or lifetime is silly if the hindrance is someone's own business needs and requirements.