it seems to me that something is missing...
Is having an environment so quiet that you won't speak more than 5 sentences on average a day cause for concern, and should I try to change it?
Being an introvert developer myself, I can safely confirm that environment like above is 200% comfortable to me. But (and that is very very big BUT), I also believe that as a dev lead, you've got a problem here.
You see, quiet environment isn't the only important thing. Even the article you refer to lists couple other points besides that one, and it doesn't even pretend to make complete list.
The problem is, the way things are as you describe, you can't tell whether your team members feel OK or are unhappy. The problem with quietly unhappy developer, in turn, is that they can equally quietly leave, following the popular behavioral pattern eloquently described in The Rise of Developeronomics article:
Rather than... negotiate with management, the talented developer will simply exit a situation he/she does not like, and use guild-like resources to move to a better situation...
Solution for above problem is pretty clearly described and explained in an excellent article The Update, The Vent, and The Disaster. This article is written from a perspective of a dev team manager and as such, it makes a good fit for your position, too.
Business is full of people worrying loudly about projects, process, and other people... but this chatter will bury the individual voice unless someone pays attention.
Your job in a 1:1 is to give the smallest voice a chance to be heard...
...you do want to create a weekly place where dissatisfaction might quietly appear. A 1:1 is your chance to perform weekly preventive maintenance while also understanding the health of your team.
...The sound that surrounds successful regimen of 1:1s is silence. All of the listening, questioning, and discussion that happens during a 1:1 is managerial preventative maintenance. You’ll see when interest in a project begins to wane and take action before it becomes job dissatisfaction. You’ll hear about tension between two employees and moderate a discussion before it becomes a yelling match in a meeting. Your reward for a culture of healthy 1:1s is a distinct lack of drama.
Note you can't safely substitute 1:1 conversation with any kind of group talk / chat. When there are more than one person to speak, you're always at risk to miss something important from someone who prefers to let others talk.
Thing worth noting is that even the passive "openness to 1:1" won't help here. "Hey if things go wrong, just ping or come to me, I'll be happy to discuss this 1:1." They may simply think the issue isn't bad enough to bother you - especially if it develops gradually and slowly... until it's too late.
- "Hey that offer from
<other team / company> sounds cool, they don't have
<this issue> at all! Why getting into trouble of raising concerns to lead (with unknown outcome) when I have an option to just get rid of it by simply accepting the offer and moving out of here?"
As suggested above, your job is to "give the smallest voice a chance to be heard" and 1:1 is the only reliable way to have that.