What if, instead, I invested $100k in a Steem campaign where I upvote people who blog about the NFL? Then, at the end of the campaign I still have my $100k + curation rewards and +/- any change in STEEM's value, and I have also rewarded some of my best fans. And, of course those fans all shared their content on other platforms because they want to build their audience and increase their rewards.

...

It's so simple, but almost no one has figured it out. I don't get it.

There are a few reasons. One is that Steem is kind of a closed ecosystem, there's very little organic spread outside of it. Advertising and PR is about getting positive stuff about your brand in front of eyeballs, not just into pixels. Another is that paid content production is much lower value than organically generated content -- there's something about money changing hands that changes the nature of the thing and readers pick up on that. Another is that many normies still view crypto as a very sketchy thing, a conventional company would probably see your "you keep your investment" point as akin to trading their money for slot machine tokens, not something their shareholders would be happy about. Plus, a small coin like Steem is probably at the higher end of percieved sketchiness. You also have the problem what other content might be "next to" your paid promotion in this ecosystem -- a lot of advertisers were spooked off of twitter after Elon Musk took over, and "censorship resistant blockchain" is even more open than Musk-era twitter and therefore potentially scary to conventional marketers.

Basically I think this idea makes sense to you because you already think Steem is good. But if you're an outsider, especially one that's conventional enough to be considering large marketing spends, then this place probably looks very dubious.