Is it time to start from scratch?

It might be best to start from scratch with the organization. It isn't yours to change, so who actually wants different outcomes from this team, and why? Only senior leadership can create, communicate, and reinforce the requisite sense of urgency for change to happen. There is an organizational gravity to overcome.

You haven't mentioned anything about goals. Dan Pink has an interesting 10-minute TED Talk (and a book called Drive) that looks at the data behind intrinsic motivation. His data shows that autonomy, mastery, and purpose are key areas that motivate knowledge workers.

Purpose: The Product Goal and Sprint Goal (both are not optional with Scrum) can be motivators. Have you introduced the concept of a product Vision and Product Goal to your Product Owner? And a Sprint Goal to your Scrum Team? What unites this team and gets them excited? If not goals, then what is it? Outcomes over outputs. So what if a Scrum Team delivers all their points, but no customer wants to use what they built? The point of Scrum is not Scrum, it is to deliver value to our customers.

Mastery: always getting better at what we do. We have the Sprint Review to get feedback from stakeholders to build a better product, and releasing often to get feedback and validated learnings from customers. Is that happening? If not, why not?

And of course, the Sprint Retrospective is another place for self-reflection and improvement. Have you leaned on the Scrum Values to help the team build trust and psychological safety? That may be a sign of why people are quiet. Also, check out the 5 Dysfunctions of a Team book. Without the Scrum values in place, would you expect Scrum and empiricism to be effective or work at all?

Autonomy: An important aspect of Scrum is self-management. A Scrum Master ought to reflect on whether the team is becoming more self-sustaining over time, or do they rely on you for everything they can do themselves.

 

Have you considered that it isn't Scrum that is not motivating them?  Could it be that the work they are doing is no longer motivating?  Is the Product they work on seen as successful?  Are they adding to it's value or just keeping it running?  Is the organization going through any changes (i.e. financial problems, lay offs, etc)?  

There are a lot of things that can demotivate other than the processes that you use to do work. It sounds to me like there is a bigger impediment impacting this team than the way that they work. 

I work with 3 Scrum Teams as Scrum Master

There are three teams, three products, three product owners, and one scrum master, correct?

It is always ok to start back up from Scratch. But the question remains, is this truly what the team needs. In you description I see lots of things the developers are doing, how they respond to situations not respecting team rules, not participating and responding.



But how are you approaching them?

Have you tried one on one coaching, team coaching? 

Or simply expressing your own feelings about the situation?



I find that fostering an environment that enables all the values of Scrum, start with yourself. Be a paragon of the values. 



- Be open about your feelings, struggles and when you need their help. 

- Have the courage to discuss the though subjects, why is this not working, what do you need, and do not be scared of silences.

- Respect your teammates by being honest and truly listening to them.

- Commit to them and with them, on sprint goals, the definition of done. But you are not their parent. Discuss with them how you can help them keep their commitments, but it is not your job to run around behind them to motivate them to finish their work. Letting them fail is also a learning opportunity.

- And lastly Focus. If you have 3 Scrum teams focus might become an issue. Show your focus by always being there fully when working with this team. But also ask yourself the question: "do they get all the focus they deserve?" if not. Then you might talk with the organization on how you can improve this situation.

If you saw the outcome changing but you never noticed what was going on in the team that led to this change, then you are not close enough to the team. As an outsider, I think you shouldn't continue working the way you did, particularly reducing the number of teams to 2 or 1. Focus on the people, not the process.

Daniel's observation is spot on, and Yannick's suggestions could be beneficial.