Why the photos are rejected?

The bird, seen here at about 300%, seems to lack sharpness and has compression artefacts around it.

But it's also 999 x 666 pixels, less than 1MP. They would all be rejected if that's the case. If on the other hand, you are uploading low quality reduced pics to test us - please don't!

Mainly, the colors are dull and uninspiring and the subjects are ordinary. For exterior shots, light conditions and time of day is important! While the compositions may be fine, there is no wow factor. Hope that's helpful and keep shooting!

The bird is underexposed:

The picture is also missing sharpness.

The snow picture needs to get a boost in the shadows. You have some colour noise, so I suspect that you have edited the picture and that you have pushed the exposure a bit. I'm missing sharpness. The power lines in the upper corner could get edited out. If you had moved the house more to the middle, you would have got a better framing.