Check out the gear most of the plugged in bluegrass bands use, and you’ll find really high end pickups and preamps. The ones who’s instruments sound good are using stuff like the Grace Felix, which costs more than a lot of people’s guitars.
The other factor with them is they’re playing loud acoustic music exclusively, with someone running sound who’s used to doing that. They’re also probably using in ears and very low stage volume, which obviously makes a big difference.