Hi! Thank you very much for your comments :)
3D printing is not only used to make useless things, it just happens that I had these objects to demonstrates the capabilities of the machines. For example, I make things for my workshops that would have cost me a lot more if I couldn't 3D print them, and we have printed a lot of PPE for hospitals during the lockdown as shown in my latest article :)
But there are sometimes also useless prints and I understand your question. Personally, I only buy bio-degradable filaments and resins (except where prohibited by regulation, like hospitals) and the objects printed with filaments like PLA and PETG can be recycled to filament or another object using machines like the ones created by Precious Plastic.
Ultimately, the goal of 3D printing is to reduce the waste of plastic, because if everyone has one, you only print what you need, reducing the waste made by traditional factories to bring the product to the consumer. And when you want to get rid of the objects you can recycle them.