I grew up in Oregon, and my folks always called them filberts. I’m not sure when I learned they were also called hazel nuts–probably when there was an espresso stand on every corner pushing hazel nut lattes. The only thing we ever did with them was feed them to our pet chipmunks. They were too darn much work to open!
I find it interesting that there is actually a botanical difference between the two. However, I know that my mom wasn’t picking through the mixed nuts saying “hmm that one is little oblong, yup it’s filbert!”. 
I guess it’s like the sweet potato/yam thing. While there are sweet potatos and yams, what we call sweet potatos or yam in the US is generally just the sweet potato.
usually just in mixed nuts.