Actually I think the title is misleading. Because overall cupidsbow doesn't argue that fanfiction makes women 'poor'. She only questions why women's hard work is so often directed at tasks that are unpaid or underpaid, and undervalued. And how does the causality work - is women's work undervalued socially because it isn't paid, or the other way round? Do women put their effort into unpaid things because they don't value themselves, or because they recognise non-monetary values? Does women's unpaid work undermine capitalism, or provide an essential prop? If it props society up, why isn't it valued?
She draws parallels between the ways that women's paid writing is denigrated (as set out by Joanna Russ in 'How to suppress women's writing' for instance) and the ways that fanfiction is denigrated.
It's easy for people outside of fanfiction fandom to dismiss the whole thing on a number of grounds, most of them described by Russ: yes, she wrote it, but we don't really know who "she" is; yes, she wrote it, but she totally shouldn't have (only perverts/stalkers/sluts/thieves write it); yes, she wrote it, but it's not important (because it's not about high culture ideas, it's unpaid, it's vernacular, it's just porn, it's derivative, it's bad); yes, she wrote it and it's actually good, but it's a one-off fluke and it's not really fanfiction anyway (it's a homage, a pastiche, a post-modern experiment, it won the Pulitzer); yes, she went on to write successful original novels in spite of her fanfiction beginnings (but she's not like all the others who do it, and let's not talk about it anyway, because it opens us up to copyright violation lawsuits).
Now speaking for myself, I read very little fanfiction, but I agree with cupidsbow that
the fanfiction community is the most amazing women's art culture I've ever experienced, and quite possibly the most amazing there has ever been, just in terms of sheer numbers and output. And perhaps that is enough.