But it's not self evident from outside the fiction. Instead, you are preferencing one mechanic over another based solely on your assumptions. That's what inconsistent: you haven't yet identified what is specifically different from a magical effect rather than the best con man in the world playing on a character's emotions. But for Bob the Vampire Lord, players have no choice but to like him after they failed their save. For Bob the Silver-Tongued, though, there's no such luck after he charms them with his diplomacy.
Equivocating the magical compulsion versus ordinary persuasion is about the same as arguing a very sharp, masterwork longsword should still do full damage to a thick-skinned creature that is resistant to slashing weapons. Sure, outside of the D&D lexicon it might make sense. Perhaps a non-magical, expertly crafted sword could overcome the resistance. But within the established 5e rules, that's typically not how it works. Could it work? Possibly, but without any consistent guidelines regarding the creation and maintenance of these extra sharp masterwork weapons, it comes down to a moment of DM fiat that could echo throughout the campaign.
Consider the following when comparing and adjudicating the effects of spells and social abilities:
Most spells and magical effects detailed within the rules are a known quantity requiring little adjudication on behalf of the DM whether they occur to PCs or NPCs . Players are usually keenly aware of their options and why they succeed or fail in these situations.
Social ability checks versus NPCs are more vague. They give the DM more leeway to adjudicate, but as a trustworthy arbiter that allows the players to act freely and put their characters' skills to use in myriad ways to avoid or overcome any obstacles or challenges, even if all the options are not explicit or obvious.
Using social ability checks versus PCs that force or heavily restrict PC (re)actions, the DM essentially becomes judge, jury, and executioner ("Your character does it because I say so.") Players are often left with little to no recourse and extremely limited options, possibly wondering if they had any agency in determining their current circumstances.
Much like the lack of rules for very sharp, masterwork swords, D&D isn't designed around precise adjudication of social interaction, especially as those rules relate to dictating player/character behavior.
Still, could a DM dictate or restrain player (re)actions simply based on opposing NPC social abilities? Sure. However, it requires an enormous amount of trust from the players. And even if the players are cooperative participants, the DM's choices will likely have huge ramifications within a campaign as the players make efforts to shore up their defenses against similar tactics or use the same measures against powerful NPCs.
