There seems to be some push back away from abstract C4D stuff lately. This piece by Andrew Serkin sums it up by making the quintessential abstract mograph animation and adding a message to STOP MAKING THEM.
Scratch Scratch Scratch
Any popular technology or trick is always over-used by beginners at first. When turntable scratching became popular, it was EVERYWHERE for a few years and then it became more subtle as DJs learned how to use the new technique more tastefully. Same thing happened with synthesizers in the 70s and auto-tune in the 2000s. 
Our current auto-tune is Abstract 3D. Starting in the last year or two, 3D has become more accessible and can now run on laptops instead of huge expensive machines. Software like Cinema 4D is made to be used by designers instead of technicians. This means more people have access to the technology and can learn how it works. More people entering a market always means a big glut of beginners that need to go though the process of learning.
Abstract animations are a fun way to learn the software without worrying too much about your scenes not looking realistic enough. In fact, I use simple abstract shapes and animations as a way to teach Cinema 4D without getting too hung up on stuff like modeling. Of course, if you want to become a real 3D artist (you know, one that gets paid) you might have to learn more than just abstract stuff. I don’t see the harm in playing and learning, but nothing let’s you know where your 3D skills stand more than a “Real” project.
We need experts like Andrew to point out the trend and to start conversations like this. However, in the end, its about being good at what you do and your ability to do what clients are paying you for. Don’t let people tell you what NOT to make. Learn, play, and make fun/abstract stuff. But, when you’re ready to learn more, remember there is much more to 3D than spheres.
1. I always use music analogies, but this happens everywhere. Look at how photography has taken off since digital cameras made it so anyone could try photography, or how Trapcode Shine is used in so many commercials on it’s default settings.
2. Also, I’m not that great at the advanced stuff either. This is a big reason why I am trying to get more Cinema 4D artists like Mike and Chris to do more advanced tutorials for Greyscalegorilla.