I had a look at your illustrations, quite cool.
First lets get the obvious out of the way - this is a volume game, you need a LOT more than just three pieces.
Now to the point - Your octopus only has seven keywords, your basketball has nine and not very descriptive, in that they don't do your illustrations justice.
Lets look at the basketball - the first keyword is "horizontal" not very specific and hardly does much by way of steering buyers to your image. I did a search with "horizontal" and iStock returned 21,493,210 results.
Thats what you are competing against.
Other keywords "bird's nest", use "bird" and "nest" seperately. "basket - ball" again seperate "basketball" and "ball". "green color" it is hardly green and yes it has color (most pictures produced diditally have color)...
Spend more time keywording but DON'T spam useless non-descriptive words that don't have anything with your illustration.
If you have an image that a client is looking for and your keywording is not up to par then they will never see them.
Here are some tools to help you:
http://www.arcurs.com/keywording/
http://microstockgroup.com/tools/keyword.php
Also more descriptive titles helps too. Simply "Basket Ball's Nest - Illustration" is a bit basic. I'd call this "Basketball in bird's nest suspended on tree branch against blue sky." or something along those lines...
Brush up on your SEO (Search Engine Optimization) and you should get better results.
On a final note, uploading to more agencies gains you a wider audience of potential buyers. Nuff said.
this is the greatest answer, i have learned a lot from it, thanks a lot