Oh Dear, I find myself about to give birth to another of my endless opinions.
TSO asks why there is a dearth of Scholarly Biographies of Thoreau. I find that there are probably three groups of reasons.
(1) Thoreau, by all accounts, was a thoroughly (pardon the pun)unlikable person. I think often of his quotation, "I would rather sit on a pumpkin and have it all to myself than share a velvet cushion." Yes--and so he sits on his pumpkin and everyone leaves him alone--I think it right and proper.
(2) Thoreau does not fall easily into the many different quagmires that amount to "victim studies." Reputable scholarly works outside the historical sciences (and even within) seem to be much more interested in publishing agenda-driven victim studies than they are in really doing research. So far as anyone is able to discern Thoreau was not gay, lesbian, trans-gendered, a member of an oppressed minority; he didn't stutter or have a noticeable physical defect; when he was in company he was not unduly flatulent or disturbed by excessive gaseous eructations. In short, a Thoreau biography would not serve to advance any of the seriously limited agendas of modern scholarship, so why waste the time, ink, and paper?
(3) Thoreau's work was primarily a work of adolescence. That is to say that his primary contribution to our understanding of the world is rooted in adolescent non-compliance. Now, that isn't to say that it wasn't put to good purpose, but coupled with statements like the one above regarding velvet pumpkins, and an almost insatiable interest in himself, this makes Thoreau a rather less than entertaining figure to consider in any detail.
Now--let the fireworks of Thoreau's admirers begin. Oh, by the way, did I mention that I am actually one of them. Civil Disobedience is a useful and necessary concept--A Week on the Concord and Merrimac Rivers is, at times stirring and lovely, as are snatches of writings here and there. And how can you not have a grudging admiration for a curmudgeon who was old at the age of twenty?