He had a living wife and relatives that could identify him easily.
True . . . but when it comes to finding a precedent for something preposterous, Russian history is almost always willing to oblige.
During the Time of Troubles, the first false Dmitry to emerge was married to a woman named Marina Mniszech. This claimant -- who actually occupied the throne for a while -- was killed in early 1606, whereupon a second false Dmitry emerged in 1607, claiming to be the first false Dmitry (although reportedly looking nothing like hiim). Dmitry No. 2 was promptly "recognized" by Marina, who went on to marry him in secret. (She apparently had no moral compunction about lying to regain the sacred throne she shared briefly with the first false Dmitry, but was rather disturbed at the prospect of living with a man to whom she was not married. Go figure.)
In fact, the saga of the three false Dmitry's during the 17th century is a striking parallel to all the 20th-century nonsense about Anna Anderson's being "recognized" by people who knew the original and to the claims that Anna Anderson knew things that only the real Anastasia could have known.
When the first False Dmitry emerged, he was recognized by the Patriarch of Moscow, who found his knowledge of court life and his "royal demeanor" to be convincing -- something that only the "real" Dmitry could have pulled off. And some members of the Russian nobility as well as foreign princes acknowledged him as the missing tsesarevitch Dmitry Ivanovich. Much as Anna Anderson, this false Dmitry was "discovered" in adverse circumstances. She was supposedly identified while in an insane asylum, and Dmitry's identity supposedly emerged when he erupted in anger after being slapped by a master into whose service he had arrived by the circuitous route of being passed from mother to doctor to monastery to temporal servitude. (Ringing any bells about dog cart rides across the steppes, anyone?)
I think the real reason there was no serious attempt to raise up a Michael pretender was that having a Michael appear on the scene would have triggered real and prickly political and dynastic issues that no one had the will or the means to confront. Raising up an Anastasia pretender would have been of no real political consequence (as almost all Russians had had quite enough of the Nicholas crowd), but it would have spawned a veritable industry for the romantic dreamers of pretty little princesses in pretty big palaces, not to mention the fortune hunters looking to capitalize in various far-fetched ways.
Unless one buys the notion that people were a whole lot more stupid in 1607 than in 1925, there is really nothing remarkable or unique about the partial success of Anna Anderson's scam. All it needed was guillible daydreamers or cynical opportunists to work . . . things which are
never in short supply.