There are so many people flexing into tank that have never played tank before or played it once upon a time like years ago. It’s ruining games. Even if you just reset the MMR for just tanks and maybe supports that help a lot. So the system could relocate them into the rank they should be in.
Community Manager Josh Nash just made a key post addressing this here:
The development team have said in the past they have no plans to ever do a MMR reset.
Doing an MMR reset would not solve this problem, it would make it much worse. Like, you’re talking about games being ruined by tank players who are not in the appropriate rank for their skill at the role, and your suggested solution is to wipe out all of the information about how tanks perform at various ranks and how they compare to each other? The mechanism by which they would get moved into the right rank from there is the same one that will move them into the right rank without an MMR reset, only the MMR reset would take seasons to stabilize.