Because Wendy's has some savage PR people in charge of their twitter :'D
Pretty much what everyone else is saying. The twitter for Wendy's had some witty comments on thing and now the internet is going absolutely nuts with the Sassy Wendy pictures right now.
They wrote a trollish comment,people found it funny and drew the mascot and everyone else followed suit cuz relevance and popularity.
Because humanity woke up and realized that perfection was looking them right in the eye the whole time.
I think they made some funny twitter posts and people projected that trollish attitude on their mascot.
Prolly because the late great Dave Thomas made her so fraiche and old fayshoned.