Comment by KwanEsq

My understanding was that that was more a function of how arc submitted stuff to Phabricator, rather than solely Phabricator itself. arc at submission time submitted a bunch of different commits as a single Phabricator DREV or whatever the terminology is/was (basically a DREV is the {domain}/D123 webpage you'd do a review on). But other tools that submitted commits to Phabricator instances (and maybe even arc itself with the right flag?) submitted each commit as its own separate DREV, so each commit got its own separate /D{N} page and its own review, but all linked together in a stack. And then still landed as separate commits in the actual repo. This is how code submission works with Mozilla's use of Phabricator.