I like to think they just feed their shit to Grimers.
Heck if I know. I think they just did it to make it look cuter. Although if you want to think of it another way, the anime usually had some pikachus with indentations in their tails who had particularly higher pitched voices. Maybe that's where GF got the idea?
IDK
Also while searching for that pic I found this:
Apparently Pikachu has a girlfriend now... and a rival? How long has this been a thing in the anime? I don't keep track of this shit anymore so what the fuck is going on? Is anyone mad because it ruins their headcanon of pikachu being a gay demiboy? Also has Ash still not won a league match yet?