Fully agree, it's not sexism it's just execs believing that "women don't sell". You hear similar things about skin colour and I wouldn't say that's racism, just execs wanting good sales.
The trouble is that this became a self fulfilling prophecy. Because higher ups believed it, not many games with women got made so there wasn't much data to look at. Then when a game with a female protagonist does badly people say that it's because of the female lead. Then when a game with a female protagonist does well it becomes an exception. I'm glad we're begining to move past that and most execs realise that most gamers just want good games.
There's a million things that make people think "it's a good game". They have to justify budgets of hundreds of dollars, so when they need to make changes they need to back with data their opinion to explain why this or that will work better. Mostly with "games that have X make more money than the ones who don't", because even inside the teams there are people with different ideas about something so they need to justify their opinions.
In this case, it's that. While ago, there were a few big games with female only protagonists every year or so, and most of them outside Tomb Raider and a few cases tanked in sales. In AC probably weren't happy with AC 3 Liberation or AC China (yes, a Vita and a small spinoff, not AAA games) just to name some example in addition to the other ones. Something that more or less made sense because their console/PC main market was mostly North American and European males, so they made mostly games targeting mostly white males.
Starting in the PS3 generation and digital games the % female console/Steam started to grow, mostly because many came from Wii, DS, browser, mobile and PS3 casual games like (in Europe) Singstar. And they started to reach new areas of the world too partly to F2P that started to become big on mobile and PC, so their demography started to be more diverse (and they noticed they were doing games for white males only and would be good to be more diverse).
They started to see some big AAA games with female only protagonist to perform well, so they are putting more female protagists (or allowing to choose a female version of the main character, or there's an editor, something that always did work like in Resident Evil, Street Fighter, etc). Same goes with skin colors, I think it was probably starting in The Division (I think it was their first current gen only game), they started to include a good amount of representation in the NPCs too. Not only Ubisoft, you can see it in other companies like Sony too. They are opening to that.
Another would be the games with dads as main protagonist. In addition of having a majority of males in console/Steam market, the average age of the players kept growing since the 8-16 bit age, back then most of them were mostly kids or early teenagers so they made games for people about that age. Now these kids now have like 30-40 years and some of them have kids (and well, same goes with the devs themselves), so they saw it was a good idea to put fathers as main characters and that taking a role in the game, someone tried it, it did work in sales so they kept doing it in multiple games like Heavy Rain, TLOU, God of War, etc. Even Marcus had a kid in GoW.
Same goes with bigger things like features, game modes, game genres, etc. They stick to what it works for them. If they see some brave team who does something differently that works, they try to replicate it if they see it isn't too saturated.
And so on. They try to do a product that they think the type of customer who buys or may buy their product may like according to the market data they have from previous similar products. It isn't something made in videogames, it's something made everywhere. It's marketing.
