Gameplay choices that are so one-sided that no one would ever pick the wrong option are actually not just a failure to create interesting choices, they actively make the game worse than not having the choice. There are a lot of reasons (I'll use the example of an underpowered race in Starcraft):
It can be intensely disappointing for players to realize that one of the game's races is useless and will never see any play, especially if it happens to be their favorite. Being disappointed is worse than not knowing what you're missing out on. I saw this phenomenon all over the place in Spellweaver.
It increases the chance of a new or potential player being turned off from the game by the appearance of complexity.
Even if they don't drop it, new players have to spend time learning about this useless race. Also the aforementioned disappointment will be a lot stronger if they had some really good experiences with it in their early days (maybe due to the training AI not knowing how to counter it).
And of course, the interface clutter of an extra button on the race selection screen. While this is a very small factor, it's not nothing.