Because why is this café named as such with 〜ので
Grammar Explanation: Objective reason with 〜ので

After having her suggestions of staff wearing bunny ears be dismissed, Cocoa asks about the café’s name.
- ココア:
- 「じゃあなんでラビットハウスなのでありますか!」
- “Well, for what reason is (this café) called Rabbit House?"”
- リゼ:
- 「そりゃティッピーがこの店のマスコットだからだろう?」
- “That's because (the rabbit) Tippy is the shop's mascot, isn't it?”