No, it was infighting, bad business decisions, bad hardware decisions, and Sega of Japan sabotaging Sega of America's efforts, among countless other things. Sega's demise wasn't because of a single mistake or bad luck, it was because they had been systematically destroying themselves from the inside since the Genesis days.
Even after going third party they still kept shooting themselves in the foot constantly until recently. Even though it seems they're getting their act together lately, I still wouldn't trust them with a console at this point in time.