It's also quite possible that lack of reviews of books by women is part of the reason why there are fewer female writers in SF. Why try to break in if fandom makes it hard (reviews themselves would be a fairly small part of that)? There's a feedback loop that's hard to break of lack of support in publishing due to lack of sales which results in fewer attempts to publish with results in less stuff published which results in lack of support which ...

Bias by reviewers by no means is the main culprit, but we all have a part to play. All participants in this cycle should be doing something to correct the problem. Putting the onus on everyone else to take the first step means that the problem never gets corrected.