pfSense

/24 is not any more or less likely to be correct than any other value. It depends on what the user is doing there which could be any number of different network sizes/lengths. Especially with custom ACLs, smaller entries are more likely to be present.

We don't default to that on interfaces for the same reason.

While that may be the most common entry for you, that doesn't mean that holds true for the majority of the user base.