The problem here is explained by Aarobot:
with the current system, you end up with utterly useless results when you're near the beginning of the time period, which, with this default, happens every week
And waffles responded with a change to partially mitigate this problem:
There is a new network wide setting (Stack Overflow is excluded) that requires an interval has 6 days of data prior to being picked, SO se sites should always default to a sane tab.
To be precise, here's how the default tab selection works:
- If the current site is a child meta or Team*, the default filter is All Time
- If the current site is Stack Overflow, the default filter is the shortest period that includes at least 1 day of activity
- For all other sites, the default filter is the shortest period that includes at least 6 days of activity, or All Time if no filter will provide that much activity (very new sites).
The week starts on Sunday. Today is Thursday, day 4 of the week. Today is the 21st day of the current month. So on most sites, the default filter will be Month, as this corresponds to the shortest available time period that provides the necessary 6 days of activity. But since Stack Overflow only requires 1 day of activity, its filter defaults to Week.
*This behavior is less than a week old; prior to that, Teams worked the same as any other SE site, which is to say they would usually default to showing the last Month of activity. Since Teams are generally rather small, this ended up being more confusing than useful.