The average attendance for a WSL game (top flight) is around 8000, but that average is skewed massively by Arsenal:
If you remove Arsenal from the equation then the WSL average is around 4300, so more than the National League (avg 2900) but less than League 2 (avg 5500). When Arsenal are added back in to the sums, the WSL still attracts less punters on average than League 1 (avg 10500) and, as others have said, that is with cheap/free tickets. The Lionesses can sell out Wembley, which is impressive, but again I believe the tickets are far cheaper than the men's games and that level of support does not appear to filter down to the club game, Arsenal aside. Perhaps women's football will be a bit like rugby in that way: Perfectly viable, and with some big moments, but not comparable to the ECL/EPL/Championship.
On one hand, it seems telling to have such modest WSL attendances even when women's football has never had so much publicity and coverage. I think it actually gets a disproportionate amount of both based on how many people actually pay to watch it, and I can't shake the feeling that is a symptom of modern media outlets and companies dealing in identity politics rather than a reflection of demand/interest. It might be that despite everything, there are only so many people interested in watching women's football, and only at a low cost. None of that suggests that Palace women need to play at Selhurst to fit all the punters in at the moment, or will need to any time soon.
On the other hand, Arsenal do get very big crowds. I am not sure what they are doing that others aren't, but it seems to suggest it is possible to attract tens of thousands. Plus, it is still fairly early days for the WSL, most clubs in which have the huge benefit of being able to attach themselves to an established men's team, with the possibility of playing at grounds that those WSL teams didn't have to build. That's got to help.
Plus, once you get behind some of the narrative-driven media coverage you find that there are some fairly hardnosed business people who seem to feel women's football is worth backing. The woman who runs Birmingham Ladies seems pretty shrewd, and the owners there are putting money in. Brighton are talking about a new, purpose built women's stadium, whatever that might mean. Perhaps it will grow. Perhaps it is already viable but just at a far lower level than the men's top two or three flights, as is the case in the National League/League 2. I love non-league football, far more than the EPL, and could imagine some will prefer to watch the women's game than the spoiled, whining idiots at the top end of the men's game. There are loads of reasons why the women's game might grow.
I was surprised to hear on this board that Parish is taking a single penny from the budget for the men's team and putting it towards the women's one. A million quid might be chicken feed in the EPL, but clubs drive ticket prices up as high as they can and cram every square inch of the ground the telly, the radio, and your brain full of adverting in increasingly invasive ways to maximise every possible income stream, so it's not like they don't count every penny. Perhaps he thinks it's worth a go to see if the womens team grows? If it did, perhaps one day it would bring in some money and could share the costs of future redevelopments at the training ground or Selhurst?
Speaking from the point of view of someone who wishes the women's game well but isn't likely ever to pay to watch it, I say they should at least experiment with more games at SP and see if it attracts more punters. My logic is that if the men's team funding is connected to it, then the club overall should explore every avenue to see if the women's team can grow.