>>27892885if they went through with their original intention and used Clefairy as their mascot I have no doubt in my mind the franchise would be nowhere near as popular.
Pikachu perfectly represents Pokemon. Its odd coloration indicates both the fact it's a magical creature and that it's an electric type. It's adorable, but powerful, which encompasses a large majority of Pokemon and guarantees appeal to both boys and girls. And though its design isn't realistic you can clearly tell it's a rodent of some kind, indicating that a large number of Pokemon are essentially animals with super powers.
Finally, it has a unique, catchy, universally recognizable name that's easy to remember. I love this little bastard.