I guess it seems real difficult due to the amount of work required to set up the tank, but if you take it a step at a time, it isn't too hard. Once the tank is up, running and stabilised, only a little maintainance once in a while would be required.
I think a lot of it is the irresponsibility of impulse buyers. "The guy that buys the blue ring at the store and throws it in the 10 gallon with his Nemo's." 90% of people who do the research are succesful. And the other 10% just happen to have got an octopus that was "difficult"
Yes they're hard to keep compared to damsels and clowns and triggers and the like. But a lot of things are considered difficult like seahorses, corals, and others, but people can be succesful with them.
They are also misunderstood but thats probably because most people don't take the time to try to learn about them. And a lot of people are scared off from them by unknowledgable lfs's and unsuccessful owners.