Because a spell creates a magical effect which is no longer a spell so cannot be dispelled. See what I did there?
You may not care, but it sounds like you are doing exactly what the designers wanted.Why should I care what the designers wanted? I run my game - not the rules, not the designers.
You may not care, but it sounds like you are doing exactly what the designers wanted.
My ruling, as DM, would give an equivalent-spell-level to supernatural effects. A harpy is a level 1 challenge, so I guess that would be equal to a level 1 spell.
Equivalent spell level = (challenge level)/2
To end the Charm or other magical effects of that nature which are not spells you would use "Dispel Good and Evil", which replaced the old school "Break Enchantment". Another spell of the same level that removes Charm is "Greater Restoration". It has less restrictions but also costs 100gp to cast. "Remove Curse" may work when other spells don't seem to fit the bill. Although it seems like 5E monsters and effects will simply say that "Remove Curse" will get rid of that game effect, even when it's something that may be a condition. Off the top of my head, an example of this would be the poison arrow of an Erinyes.Then the better question would be: how does one dispel a non-spell magical effect?
It does when I, as DM, say it does.
Why should I care what the designers wanted? I run my game - not the rules, not the designers.