I'd like to see the raw data for that study, as we could pretty much make some predictions that would settle some debates.
To summarize, they found that male-only games had the biggest budget (call this 100%), followed by dual-choice protagonist games (80% of the baseline), and female-only protagonist games getting the lowest budget (50%). The split was 50/50 between male-only and male/female games, with female only games getting a "whopping" 4% of games.
One question we can ask is whether those dual-protagonist games are male-oriented with the female choice stuck on as an afterthought, which I'm guessing is the general "default" viewpoint, since "male is the default" etc etc. But consider this, if you're pitching a female-only game and you ADD a male option, you're almost doubling the average budget they throw at you, whereas if you're starting with a male-only game and add a female option as an afterthought, the statistics suggest you're lowering the potential budget they will allocate to you. So, from the perspective of how it affects your budget proposal, it'd make a lot of sense to convert a female-only game into a dual protagonist one. Hence, a LOT of the dual-gender games could have started out as a female-only concept, with the male as an afterthought to get it funded.
As for the raw data - it's fine to tell us that male-only protagonist games have a higher average budget, but what would be more convincing is to see the comparative sales figures for games that had the same budget.
There are games with both high and low budgets, and both male and female protagonists, so we can compare apples and apples, rather than apples and oranges - i.e. the chicken-and-egg question. Do male protagonist games sell better because they have a bigger budget, or do they get a bigger budget because they're better sellers - specifically, are they better sellers when the budget is equal.
If games with a male protagonist outsell games with a female protagonist when the budgets are equal, then that would explain why they allocate more budget to male-protagonist games purely based on the profit motive, rather than "they're dumb" or "they're sexist" or they're just "not thinking outside the box".
On the other hand, if games with a female protagonist are really under-represented - in MARKET terms - then you'd expect games with a female protagonist to outsell ones with a male protagonist - when the marketing spent on each is completely equal, purely because they're so rare, you'd expect the few examples to sell especially well for the amount of market exposure they get.
So, having the actual raw data would allow us to fairly conclusively choose between these scenarios.