It's not because they're secretly getting back into making consoles
A new Dreamcast trademark filed earlier this August by Sega itself caught the interest of gamers who extrapolated theories of the former console maker's intentions. The natural reaction was that Sega might be actively pursuing console hardware production again with a new Dreamcast-branded machine.
Alas, Sega of America's PR director Charlie Scibetta refutes the speculation, explaining that his company's re-filing of the Dreamcast trademark was simply to ensure that it maintained control over it.
"SEGA has no plans to get back into the hardware business, but we also want to protect our past and current brands. The trademark application was filed to protect our current and potential future use of the word DREAMCAST and to prevent other parties from using it in a way that could be confused or linked with SEGA."
The "potential future use" part does allow us to dream, of course. If console hardware is out of the question, then re-distribution of Dreamcast software over current console online services remains a possibility.