When a woman refuses to have a first date paid for it seems to communicate that she wants plausible deniability to be able to insist that the interaction was not in fact a date, or romantic in nature, in the event of non-attraction. It's generally a good sign for a man if a woman accepts his offer for payment of the date since this at least indicates that she is willing to acknowledge the interaction as a "real" date, and as a bonus she isn't too militantly feminist.
While none of this is economically ideal, it's generally the impression I get within the context of the society I am in. Women can avoid communicating disinterest while offering to split the bill simply by being congenial while declining the offer for the man to pay, or suggesting splitting the bill in a friendly, lighthearted manner. When women are too aggressive in insisting that the man not pay one cent of her portion of a bill, that's when it comes off as rude or a sign of disinterest.