Because they know that in Agile there is not boss or manager or any kind of Chief. However, many companies try (it is a waste of time for me) to reconvert team leaders into Product Owners or even worse in Scrum Masters.
First of all, a team leader working as Product Owner will order the team to finish every user story in the Sprint Backlog without care the estimation of team members.
Secondly, team leaders (or managers as well) can work as Scrum Master because they always assign tasks and requirements and set deadlines based on their own feelings and knowledge so they are the worse candidates to fill out the role of Servant Leadership. Furthermore, they love the old fashion way of management of “Command and Control”.
Command and control
Using this approach, team leaders consider team members are dull guys (forgetting that they were hired as skilled and smart professionals) and, of course, guys realized about that.
If you trust on someone you should delegate tasks trusting on their capacity to deal with them. On the other hand, when you don’t trust anybody, you will ask for status many times per day and meet with them to check their progress.
There is another huge issue with Agile: if you are converted to fill out the role of Product Owner what will be the next step? Chief of Product Owner, it would be feasible only if the company adopts Scrum of Scrum and then what?
What about for Scrum Masters?
Imagine that a team leader (or manager) accept to work as Scrum Master. What can he expect for his professional career in the company? Become an Agile Coach? Well, these and other thoughts are in their mind.
Human resources of Agile companies have to research how to motivate this new role if the companies want to move team leaders to act as servant leadership (or Product Owner).
To conclude, working with Agile roles is a big challenge for companies and that plan to shift from Waterfall to Agile!!!