Everything pertaining to significantly increased freedom for females gets very little exposure, so most people have not heard of female separatism. The people who are most likely to promote female separatism, radical feminists, are blindly hated and widely misunderstood, so people, even lesbians, will dismiss us without listening to what we have to say about the subject. Among those who have heard about female separatism, there are probably lots of strange and false ideas about what it entails (such as the person below who thinks that separatism involves refraining from going to the grocery store just because men are there).

Separatism is unpopular for the same reason that anarchism is unpopular—they both involve seismic shifts to the current structure of society. The majority of lesbians—just like the majority of people in general—probably want to live in the society they are used to, with just a few tweaks to that society so that they aren't mistreated or disadvantaged. People get attached to what they are used to, even if it's worse than the alternative. They may desire the advantages of separatism, but, I've found, those advantages don't occur to them; someone has to explain the advantages because people generally aren't used to thinking outside of the structure of the society they live in.

Also, a lot of women are now insulated from the brutality of patriarchy, which might otherwise increase their interest in separatism. Because women are now able to hold jobs, own property, be out lesbians, etc. without too much trouble in many parts of the world, living in a more integrated fashion with men does not much bother them. The socioeconomically privileged aren't experiencing the more overt and urgent predatory male behavior that many homeless, incarcerated, disabled, and prostituted women face, and they aren't poor enough to experience the reality that all the advances in women's legal rights don't translate into stable, well-paying employment for many women (which drives the prostitution, poverty, etc. that make women vulnerable to male violence). Other legal advances have made men afraid of losing their jobs, going to prison, etc., so they may turn to misogynistic porn, abuse prostitutes or runaways, or even fly to Thailand to rape children instead of taking out their disgusting urges on women in the Western world. The male brutality has simply shifted out of view relative to places where females have no choice but to live with and marry men and be continually exposed. Some women don't even see feminism as necessary anymore.

In the United States especially, people tend to have a blindly individualistic perspective on society. Women don't view their position in society as connected to that of other women enough to prioritize sharing resources with women instead of with men, and doing so is not the norm and will therefore seem odd. People do their own thing, separately, and hope the government will fix everything instead of addressing it ourselves. Collective political action in day-to-day life is foreign to a lot of people; they view it as activism, as separate from how they live their personal lives. You do activism or volunteer and then you go home and live your life; you don't live activism 24/7.

And people tend to not think of women's welfare in terms of material resources. Politics is seen as a lot of talking, arguing, voting, and passing laws. People "raise awareness" (i.e., talk) rather than just putting some money in some poor woman's hand. Of course there are issues with simply giving out money, but my point is that increasing women's collective resources is far more effective than talking about women's issues.

I could go on. The bottom line is that lesbians aren't that different from other people in their worldviews.