أَنَّ «هَلْ» بِمَعْنَى «قَدْ» فِي الْأَصْلِ
That hal is, in its original analysis, associated with qad.
A grammatical-rhetorical account associates hal historically or analytically with qad, with the interrogative function superimposed. Since qad is strongly associated with verbal constructions, this is used to explain a preference for verb-first patterns after hal.
This is an analysis debated within the discussion, not an unqualified rule to impose on every occurrence. Other explanations appeal instead to question focus and the effect of fronting.