Looking at this from a purely financial angle, it still makes no sense. Companies know that investors tend to pull away when they see backlash of this magnitude: It shows that the company is making poor decisions and are out of touch with their player base. This is largely why World of Warcraft had begun failing after the Activision Merger when they had to buy all of their stocks back from Vivendi. The company started to cut costs and their investors began to bail one after another. If SE is after money, this was NOT the way to go about it and they should have learned from Blizzard Activision Inc.'s mistakes.

The money it would have taken to create the female and male counterparts of the races would have brought in far more revenue than it would have cost to create the content and possibly brought new investors on board, or kept current investors interested. It would have sparked respect and admiration from players in other MMORPGS such as Warcraft to make them check out the game after seeing how the Devs cater to the community in this game. All around, gender-locking LOST SE a lot of money. As this backlash is making more new players wary of joining the game altogether - when they would have otherwise purchased the game and new expansion.

"If they're making their current fan base so angry... why should I join the game?"

This is not a question you want to leave potential customers with.