Our FC is a little unusual as it's specifically for people with Social Anxiety. We do have Discord but use it mainly to keep in touch outside the game, voice is just for call-outs on higher end duties.
Anxiety is definitely one reason why people don't use voice. We're happy not to use voice for general chat as it means nobody gets left out of the conversation. Female players often avoid voice because they don't want to be harassed or treated differently because they are female and sadly, that still happens quite often.

I think it's a good idea to ask about voice when you are considering joining a FC, some use it a lot, others like us don't. There isn't a right or wrong here, you just have to find a group that works in a way you're comfortable with.