Why was Yeri added to Red Velvet?

Yeri added nothing to RV and she never ended up even being a popular maknae so why did SM put her in? She is also the weakest dancer and singer in the group.

for visual,variety and she's not the weakest singer nor dancer.

Someone said to bring down the overall age of the group and her personality. Idk

its 2022 and people are still hating on Yeri and questioning her addition, get a job freaks