You made me chuckle for the day. I fought with my colleagues for years trying to convince them to always read the literature before they did their lab work. But more often their experiences matched yours. They would do the hard work only to discover they had reinvented yet another wheel. Rinse and repeat over and over.
The odds of designing a truly new audio amplifier are incredibly small unless you use new physics, maybe superconducting wires or something more exotic. Using off-the-shelf components has been done.
Yep, when you think you've come up with the latest and greatest whigget, you do a search an find out someone already did it to keep their pet tyrannosaurus rex from wandering too far from its cave.
Or if a new requirement, such as a safety requirement is imposed on your company's products. I've seen that sort of thing trigger the creation of valuable and patentable solutions. The rub is that you and dozens or maybe even hundreds of others around the world are trying to solve the same problem with similar resources and constraints and often with similar backgrounds.