That's a pretty bogus comparison, whoever made this. First of all, those cartoons on the top are from a period as long as thirty years, sixty years if they're including the Simpsons and Ren & Stimpy. The lower half includes cartoons from 2010- 2016, a mere six years. Of course certain visual trends will dominate cartoons from decade to decade. So they're comparing the visual differences of sixty years to six.
Another thing is that they're comparing theatrical-level productions to TV shows that are on a tight timetable. Of the ones on top, four of those are TV related - one by a guy who never finished on time or on budget, a show that was the first animated sitcom, a show that provided a huge boost to the fledgling FOX channel and was a breakout hit, and one with animators who had decades of experience who could make the most of a mere 2,000 drawings.
Furthermore, while more visual variety is always desired, I'd find it hard to believe anyone but a more unacquainted viewer could mistake Craig McCracken's current, bold, flowing, lava-lamp like style for C.H. Greenblatt's early 70s looking sketchy visuals. Or Hartman's lame imitation of 1950s angular character design for Ben Bocquelet's melting pot of anime, graphic, and multimedia inspirations. Or Chris Savino's more raw, newspaper comic like designs for Alex Hirsch's more lush, but uninspired, geometrical characters.