I think the answer to that is Hanna Barbera.
That is an animation company that produced a LOT of cartoons in the 60s and 70s and well into the 80s. They did their work on the cheap. Minimal budget, minimal time, minimal frames per second.
They did produce a lot of stuff that is appreciated and loved to this day, like the Flintstones, Wacky Races, Scooby Doo, and the Smurfs. But along with that they made a lot of forgettable junk that was not high quality.
The original Warner Brothers cartoons with Bugs Bunny and Daffy Duck, back in the 40s, they set a VERY high standard, they were imacculately made cartoons full of sophisticated humor.
For a few decades after that, many cartoons were cheap and disposable.
In the 90s, there was a renewed appreciation for the artform, an understanding that cartoons were not simply disposable entertainment for children. There were now "adult" cartoons like the Simpsons, and avant-garde cartoons like Ren and Stimpy.
The difference between cartoons from the 60s and from the 90s has a lot to do with how the artform of animation was received and appreciated at the time.