Nothing's wrong with cartoons today. Everyone thinks the cartoons they watched as a child are the best. When you're an adult, most kids' cartoons aren't going to do it for you, because... you guessed it, they're for kids. And most kids' shows aren't going to be that enjoyable for adults unless you have nostalgic value for them.* My childhood was in the 90s, I absolutely loved most cartoons I saw then. Conversely, I think most cartoons from before then are dumb - Looney Toons, Tom and Jerry, etc. are ridiculously stupid to me. Then again, so are most modern cartoons. I guarantee kids these days in ten, twenty years will bemoan about how their childhood cartoons were superior to the garbage kids of the future are watching.
*There are exceptions to the "kids' cartoons are dumb" rule. Some cartoons targeted toward children are truly masterpieces, and can equally be enjoyed by adults. And some adults simply are capable of enjoying children's stuff more than others, nothing wrong with that either.