This may be due to the fact that the "cl_teamid_overhead_always 1" command increases the amount of detail that appears in your field of vision. It could be distracting to some Pros and take away from their ability to play the game optimally. That being said, why don't Pros use it is ultimately up to each individual, depending on how they prefer to play.
Here's some additional information on the "cl_teamid_overhead_always 1" command that may be helpful to understand why Pros don't always use it:
cl_teamid_overhead_always 1 is a console command in Counter-Strike: Global Offensive that displays teammate colored overhead names and health bars above one's head. It does not, however, provide any additional map or game knowledge.
This command can help to better differentiate teammates from enemies in close quarters combat. It can also be useful for highlighting where squad mates are on the map when playing with more than one player on a team.
For some Pros, the extra amount of detail can be a distraction from focusing on the task at hand. As such, many choose to not use the command to keep their focus on the game.
In short, Pros don't always use cl_teamid_overhead_always 1 because of the amount of detail that it adds to their field of vision, which could be distracting and hinder their ability to play optimally. It ultimately comes down to each individual's preference and their own style of play.
