In 1e AD&D, p.37 of the PHB to be precise, under "notes" in the weapons list, there are a lot of "includes X, Y, Z" entries, where X/Y/Z are other weapons similar in shape and type. In other words, they lumped weapons together.
Most of these are polearms where they lumped some minor variations under the same blurb, but under Scimitar, it says "includes Cutlass, Sabre, Sickle-sword, Tulwar, etc." (basically, any long curved bladed weapon used scimitar stats). Basically, they lumped the sickle under the scimitar heading. Since they wanted druids to have access to sickles, it meant (in game mechanics terms) giving them access to scimitars.
After that, it sort of just became the de facto weapon of choice for druids, since the scimitar was better than all their other choices. It stayed on in 2e and even into 3e, although now that we actually have a true sickle on the weapons list, the original reason for the scimitar being a druidic weapon is long gone.
It's just a hold over from 1e days, and everyone seems to like it so no one has rushed to change it to something more historically accurate.
Side note: I believe the khopesh was made a druidical weapon because it too is shaped a lot like a sickle. It looked funky and exotic, so it was made druidic. Weird logic.
Most of these are polearms where they lumped some minor variations under the same blurb, but under Scimitar, it says "includes Cutlass, Sabre, Sickle-sword, Tulwar, etc." (basically, any long curved bladed weapon used scimitar stats). Basically, they lumped the sickle under the scimitar heading. Since they wanted druids to have access to sickles, it meant (in game mechanics terms) giving them access to scimitars.
After that, it sort of just became the de facto weapon of choice for druids, since the scimitar was better than all their other choices. It stayed on in 2e and even into 3e, although now that we actually have a true sickle on the weapons list, the original reason for the scimitar being a druidic weapon is long gone.
It's just a hold over from 1e days, and everyone seems to like it so no one has rushed to change it to something more historically accurate.
Side note: I believe the khopesh was made a druidical weapon because it too is shaped a lot like a sickle. It looked funky and exotic, so it was made druidic. Weird logic.
