Harper is a victim of a chronically f*cked WWE system in which creative freedom is verboten.
Dave Meltzer reported that Harper was blamed for Braun Strowman's botch at the WrestleMania 35 André The Giant Memorial Battle Royal (!), and that Vince "hated" his (favourably received) Axxess match with Dominick Dijakovic. That is a weird tidbit: the f*ck is Vince doing watching Axxess matches, when he, in Triple H's words, doesn't even watch NXT? Moreover, Vince wasn't happy with Harper's post-'Mania dark match with EC3, either. He "hated" the Drake Maverick spots the agents came up with.
In TV masterpiece The Wire, Homicide Detective Jimmy McNulty is loathed by his boss Bill Rawls. McNulty claims that Rawls has "a hard-on" for him, in this context meaning a grudge he spends a disproportionate amount of time dedicated to upholding.
It seems this phenomena applies to the Vince/Harper relationship.
Where McNulty's maverick, not-by-the-book methods informed Rawls' hatred, Harper's inability to speak in a southern accent has informed Vince's. It's an oddly specific stance from which Vince will not be moved. Harper is of course a great pro wrestler, an agile colossus with offence that is legit jaw-dropping - Skinner, but great.
Vince pushed Skinner more than Harper as a singles player.