Bethesda made the game and the DLCs, and they can unmake them if we want. We should appreciate the wonderful content they're already given us..
I think part of the reasoning for them was that we have a lot of fantastic mods out there that are practically DLC quality. Anyone here play the Agent of Righteous Might mod? If you haven't, do it (unless you don't have a PC). It's huge, fully voice-acted, has great writing, and is overall just excellent. It's these kinds of things that Bethesda has taken note of (in fact, I believe that Hearthfire is just a more official and expansive release of a mod someone had already made). This is also exampled in some interview with an employee about why you can't use spears/be a werebear/fully control dragons in Dragonborn. He commented that the team was leaving it up to the modders. Stupid? Yes, but it shows that they have a lot of faith in modders.
I really do believe there should be more DLC. I think there should be two more: one about the Falmer/Dwemer, and one about the Thalmor. These two particular story elements are very untapped, especially the latter. But, then again, there's a comprehensive mod series of quests fighting against the Thalmor (forget its name), so why should Bethesda have to do it? (sarcasm)
Regardless of these issues, we can't force Bethesda to work on Skyrim so much. They slaved over it for years, longer than most games nowadays, and made two incredible DLCs. Many games nowadays are in much worse shape than that. If they want to work on something else, that's their choice. If they chose to discontinue the entire Elder Scrolls series, that'd be a major problem.
So for now, let's stop rioting, and wait to see what the future truly has in store for us.
And for those people saying that there's a lot of money to be made, screw off. I've only been a Bethesda fan for a year, and I can see that they aren't the kind of developer to let money compromise their integrity. I'd rather they make few truly brilliant works with a lot of passion than many cash-in works just for money.