@Victor Hugo248276400thd , it is true that professional photographers need to understand copyright laws, what is permissable for commercial sales and what requires model and property releases. Realise too, that when your photos are accepted at any stock site and people start buying your images, that makes you a professional photographer.
The concept of copyright is to protect the artist and their intellectual property and not have other people profit off of their creativity and work. Everytime you take a photo, that photo is your intellectual property and it is protected. However, when you are taking photos of a subject that someone else created, you are infringing on their intellectual property if you try to sell it and make money off of their work. You are free to take photos of art and buildings in public places, but you are not permitted to sell them and make money off of those images.
Regarding your photographs you submitted, the first image of the metal flower sculpture appears to be a fairly modern piece of artwork which would be protected by copyright laws. Besides that, there is an image of a woman clearly identifiable on the billboard to the right of the photo - she would also have to sign a model release for you to permit you to sell her image.
The second image of the statue in the pond, may be old enough to no longer have copyright protection, but it looks like the location could be a paid venue like a botanical garden. The moderators wouldn't know if you had to have a ticket to get in or not, so they will err on the side of caution and reject it. Ticketed venues require you to get a property release from the venue if you want to sell your photos for commercial purposes.
The last image of the street scene has multiple IP violations including the Carni Justino business name on the building and on the truck along with the cow logo and logos for Instagram and Facebook. The vehicles would have to have their license plate numbers removed along with any insignias and logos. The Apple sticker on the back of the van would also have to be removed.
Stock photography needs to be generic enough that it can be used by multiple buyers. When you submit an image you are clearly stating that you have the rights to everything seen in that image or you provide model and property releases giving you those rights. It does seem overwhelming and complicated at first, but when you familiarise yourself with the rules it becomes much clearer.
On a different note, I think I should mention that your images also have technical issues that would probably prompt rejections as well. It looks like they were taken with your phone's camera. Smartphone images are accepted for stock, but are held to the same standards as all of the other images. Most of your images have a lot of noise and artifacts in them. There are also portions of the images that lack detail and have a "painterly" look to them. Take a look at this portion of your image viewed at 100% magnification. Besides the lack of detail, the sky is also overexposed.

I hope this explanation helps. Take a read through some of the links that were offered earlier on property releases and model releases. Best of luck with your future submissions.