I've noticed similar trends and have came to the conclusion that the reason for it is the vector graphic and Adobe Illustrator. The designs we're seeing in wide use today are either really easy to make in illustrator or something old reinvented vectors. Logos have to be resized, so naturally Illustrator is the tool of choice and vector graphics are the file format of choice. Hence, lots of filled circles because circles are easy to make in Illustrator. It's design laziness.

Similar, other common patterns like the way over done florals, are the result of a few people making the effort to vectorize old font foundry ornaments from the early 1900s, when there were massive books filled with these. There has been a limited supply of nice looking vector ornamentation and high demand. So designers keep reusing variants of these same ornaments over and over again, blacking them out, filling them, and if they're feeling particularly creative using gradients. It's a bad art nouveau renaissance.

Worse yet we have to look at florals and grundge mashed together for no particular reason, other than that the dodge and burn tools are easy to use.

The good news is, people will keep coming out with new vector art and that will push the design art along.

The bad news is the most common and widely used tools in Photoshop and Illustrator will continue to heavily influence the designs.

What we really need are new and exciting tools.