Power outages occur, and you probably want the time to be correct when the power comes back on.
The reason these clocks are so bad is that they use bad RTC units to save a couple dollars. A bad RTC can be had for pennies. A good one (like a DS3231) is $4! Thus, we are all stuck with bad clocks; AC powered or otherwise.
GPS/NTP/WWVB exist to get the time right initially. A clock will be wrong if you set it to the wrong time, even if you have a perfect frequency reference.
The reason these clocks are so bad is that they use bad RTC units to save a couple dollars. A bad RTC can be had for pennies. A good one (like a DS3231) is $4! Thus, we are all stuck with bad clocks; AC powered or otherwise.
GPS/NTP/WWVB exist to get the time right initially. A clock will be wrong if you set it to the wrong time, even if you have a perfect frequency reference.