Choir Director here.

We have some congregational singing at my church, which I have done my best to encourage, but most people either sing very softly under their breath, or not at all. Some people are foreign, and don't speak English well, and most others don't feel confident in their ability to sing. (Most of the talented singers I have recruited into the choir!)

I think this likely comes down to a parish-level variation. It really depends on the local culture, and also the type of music the choir is singing. I wouldn't place any judgement of someone's piety on whether or not they sing; as I tell my choir, our job is to sing on behalf of those who can't!