must-staple requires additional effort from server operators, which is very challenging to roll out. This new scheme can be implemented by the browsers and CAs

must-staple requires additional effort from server operators, which is very challenging to roll out. This new scheme can be implemented by the browsers and CAs together, which is vastly simpler than having every webserver in the world turn on OCSP stapling. There isn’t any particular force driving for OCSP stapling: Browsers can’t turn it on until it is ubiquitous. CAs don’t want to enforce must-staple because their users will need enormous amount of help rolling it out. Site operators don’t care if browsers are fetching OCSP (especially since Chrome and Edge don’t)