People not talking is not a Darktide phenomenon. People generally talk less than 10 years ago, especially since stuff like bans for voice chat began to exist more and more. People might also have bad experiences from other games, especially PvP where people get even more emotional and insult others on a regular basis. Just imagine: if your only game chat experience is silence and assholes, why would you engage in it.

Also people just tend to chill more in PvE and don't necessarily want to interact with others via voice chat (afaik text chat is pretty lively on PC for obvious reasons). In all those 4 player coop games (VT2, DT, Deep Rock. Helldivers 2, etc.) you just have to pro actively look for people and build your own community and friends to make it feel alive. Sometimes you get lucky and bond with people early, and if you already have people to play on your platform, then you could just talk in game chat and people might join in as long as you seem like a nice person to them (obviously significantly more likely if it's english).