How can a violin limit you to a grade?

Hello. I’ve been wanting to buy a violin, and have heard that you can’t get past grade 5(no idea how advanced it is) with some violins.

I know I might be thinking too far, but was curious.
How can the violin limit you to a certain grade? Is it just the tone or something else?
Thanks for your replies. I still don’t know who is right at the moment lol.