¿Por qué me han rechazado cada una de estas fotos?

[Benito261647932wod]

[Jill_C]

Soft focus, lack of detail and artifacts, probably from a camera with a small sensor (mobile phone?) are the most noticeable issues. The final image would have needed an IP release for the statues.

[Benito261647932wod]

tomadas con una cámara Canon 550D (18Mp) ¿Los artefactos pueden ser un letrero en la primera foto? Si enfoco más creo que sale algo de grano ¿?. 

[Jill_C]

That's a 12 year old crop sensor digital camera, one of Canon's earliest; while it's not impossible to get decent images under good light, the high ISO performance is dismal. If you're still using the kit lens (probably an 18-55mm lens), sharp focus is challenging to achieve. (I know because my first digital SLR was a Canon Rebel with 18-55mm lens, which I upgraded soon after I got the camera.) 

Blur could also be caused by a shutter speed that is too slow, a poorly calibrated lens, camera or subject motion and not using a tripod. 

Grain / noise isn't caused by poor focus, but is more likely caused by high ISO. 

[John PDX]

I've had photos accepted that I shot with my Canon 70D.  It's only a little newer than your 550D.  I think your body/sensor should produce adequate images with good lighting and a quality lens.  A 50mm prime would be an inexpensive option.  I've had good luck with the 18-135mm STM lens.  As Jill said, the kit lenses are not good at all.  If you have the budget, the Canon 24-105mm f4 L series lense is very highly regarded.  It's also compatible wih full frame bodies so you could continue to use it if you upgraded to a full frame Canon body (e.g. 5D, 6D).  The 5D series II and above take excellent photos.  Best regards, John

[Jill_C]

Agreed. The 50mm prime (also known as the "nifty fifty") is a very nice lens and quite inexpensive. I still have one even though I have several expensive L lenses. I also had the 18-135mm for a while which was the kit lens with my Canon 7D, and found it to be reliable and versatile. And I love my 24-105mm L Lens - it is my "walking around" lens, and my primary travel lens because of its versatility. I've taken probably 100,000 images with that lens alone.  

[John PDX]

I agree with Jill.  Also, I think the two duck photos are underexposded, especially the second one.  That should be correctable.  The trick is to lighten the image without making the glare on the water overpowering.  Raise the midtones and shadows but not the highlights.  
Lastly, the first photo shows a company name in large blue letters on the side of a building.  That will need to be edited out or else it will be rejected for an intellectual property violation.