Various typically smaller changes have difficulty getting acks from all relevant maintainers. It is often quite reasonable to not wait long with such, and pinging - besides often being fruitless - may also be excessive. The possibility to “fall back to THE REST” is also fuzzy at best. Furthermore what gets (or doesn’t get) committed would also be nice to not depend on the particular committer, but be (somewhat / more) predictable / consistent across committers instead.
In this context also remember that the chasing of acks is generally the job of the submitter, yet in particular infrequent submitters frequently won’t do so (possibly because they don#t even know).
Main intended audience here are the committers, without any intention to restrict this discussion to just them.