And I pointed out that 2 monsters in the MM from A-D have intimidate, and 4 have persuasion. Not one Angel, Demon, Devil or Dragon can has the intimidate skill. And only 4 dragons(3 of which are good) have persuasion. 85 monsters and only 6 have those skills.
If these skills were supposed to be used against PCs and not say for use against other NPCs or to inform the DM on how to roleplay them, many more monsters would have those skills. I mean, the whole devil schtick is to persuade people to make deals, except not one of them is actually proficient in it.