I know this because I read them when I was younger, pre-internet. Peanuts can't compete in a world of abundant webcomics. They range from the top to the bottom of quality, but given their sheer quantity, that means there's an awful lot of the "top" out there. The only syndicated strip I know that can stand up next to the top webcomics is Calvin and Hobbes.
(And even then, while the line art stands up, many webcomics' coloring blow away what Mr. Watterson was capable of doing in newspapers. Please note my phrasing on that; I'm blaming technical limitations, not Watterson's ability. IIRC he had some watercolors or something like that he'd done in the back of some of his books... his skill was beyond what newspapers of the day were physically capable of showing.)
A few of them still manage to do some good work, but great work is almost physically impossible now.
And if what you want is merely good work, there's probably a dozen "good" webcomics now for every "good" syndicated comic out there. In fact I think I stumble on a "good" webcomic every three months or so, only to notice that it has 5+ years of archives available. (I do this on purpose; in many cases, the webcomic that is "good" when I find it really wasn't particularly good in the first couple of years.)
Also, the collection Chip Kidd designed is a great doorway into understanding how it could have become so popular. [1]