Wholeheartedly agree with you.
You are forgetting however that thanks to our public school system and the advent of mobile devices and computer games... I think kids these days either can't read or don't even think of it as an option.
Which pretty much leaves the adults pursuing it out of nostalgia.
I never had allowance growing up or family members buying me comic books, so I never got any exposure to them.
But I devoured the funny sections of newspapers anytime I could get ahold of them.
So for me: that's my nostalgia.
I think digital platforms are here to stay and for cartoonists (and comic artists) to be successful, they need to start looking for a way to marry their craft to digital media.
I think I have finally reached the point where buying a paper book is less appealing than having one on my phone in my pocket at all times to be read when I have the time.
I even have started looking for digital kids books to read to my son when we are stuck waiting somewhere.
But a cartoon work on a digital device needs an entire new approach to layout and readability.
Our screens are mostly small and the layout needs to be less busy in order for the reader to be able to follow the content without our eyeballs popping out of our skulls.
As far as your graphs of attention spans for entertainment: I think that also will only get worse.
People just don't want to get invested in new content anymore it seems, and are looking for bite-sized entertainment or the next flashy thing.
I run my cartoon-off contest cause I have a deep appreciation for the unique ability the cartoon has to communicate how no other medium does, and it makes me happy seeing these artists get rewarded. Maybe most of all because as an artist myself I've experienced plenty how hard it is to get those precious moments of feeling as if your craft has been witnessed and appreciated.