Ah, okay. :)
The WMF performs banner tests throughout the year, as part of its efforts to maximise the banners' effectiveness. A/B tests. When that happens, a small proportion of users is shown the most recent fundraising banner designs, and then the designs they've run are compared for fundraising effectiveness.
I haven't seen any such banners here my end in recent weeks, so I think you may just have got caught in the test group. The big fundraising campaign is always in late November and December. (Come to think of it, I think there may also be some countries where the banner runs at a different time of the year.)