I am at a loss as to why my work is not accepted.

There are some areas that could have been cleaned up, a couple of objects that seem very random on unrepresentative of anything in reality. Some of the plants and flowers aren't casting any shadows, which make them look like they were just pasted in.

Reasons for rejections:

• https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html

Compare your work with current Stock inventory.

You're competing with 39 million abstract wallpaper/background images, not to mention millions more free ones from other sources.  Sorry but this category is a waste of time if you hope to sell anything.

Find real subjects that buyers are interested in paying for. 

Did you do any upscaling? The images are all quite soft. Additionally, I would question what the commercial appeal of such images is. What rejection reason was indicated by Adobe?

Владимир, это тот уровень который загружался на сток около 1,5 года назад, сейчас уже требуется другое качество. Плюс в изображениях есть мелкие неточности. Посмотрите "Анализ прибыли" сверху на странице в Adobe Stock и посмотрите какие именно фото и иллюстрации хорошо продаются и имеют коммерческую ценность.

Some comments by a quick view. The first one the center is blurrred, the second lines are flat where they should be rounded , the third one the trees and plants are not connected to the ground but seems to be 'floating' above.

Hi! For all rejected images, a reason is given. You can look at the tab "Not accepted". 
In your case I can assume that abstract images have low commercial value and the supply of such images clearly exceeds the demand. 
Adobe Stock has an excellent help where you can see information about the type of content that is in demand and have a high value.