Why Errol Spence Jr. and Terrence Crawford are not fighting: Top reasons why welterweight unification boxing match delayed

Everyone wants a Errol Spence Jr. vs. Terence Crawford fight. So why hasn't it happened yet?

source https://www.sportingnews.com/us/boxing/news/errol-spence-terence-crawford-not-fighting-welterweight-boxing-delayed/aolc4nkzx2w8qrw42riz5kmy