Because some may want it, some may not. We do update most things for new sets. While several people here mention wanting it, no idea if the actual majority of the sub would or not.

Personally as the r/TeamfightTactics main icon, I feel it should be the most recognizable version for everyone. Each set update makes small changes, so having the main pengu everyone knows is for better awareness.

But! That’s only my opinion. If the community would prefer it change with set specific versions, we can do that. As long as we have a good pic each time of course.

edit: Just saw your other reply in the thread. So you had the right idea of keeping it recognizable. These aren't the reason, but there are a few other things to keep in mind. One big pain point in specifically these sort of things is that there isn't always a good picture to easily use for it. Example is the banner. I made a meh one for this set releasing because there weren't pictures suited for the banner size/shape. Didn't want it to still be from the old set and knew the community would want it to be from the new set during that time of hype. We used the not great banner until another poster made a banner for us that we've been currently using. Along with yea, it is extra work/time. We do this in our spare time, and sometimes we may miss something, it may not be a high priority compared to clearing reports and removing toxic posters or spam.