Rationale for persistent UI elements that is overlayed onto video windows

With a lot of people now using video conferencing tools, there has been a lot of articles highlighting the usability of these applications.

Microsoft, which boasts a very large research and design team, has been getting a lot of criticisms around the tool bar that seems to be in the way, at least judging by the number of posts on their MS Teams UserVoice site:

While it seems like something that should be easily picked up in any kind of user testing, the fact that it is still there suggests to me that there is either a technical constraint/reason why it is there, or if there is also a practical or user requirement reason why it is designed and implemented the way it is.

So my question is, is there a design benefit for a persistent tool bar on a video conference application window? Compared to other video conferencing applications, is there a reason or purpose for this design decision?