The way I see it:
Our bodies and the systems for energy consumption, storage and utilisation were designed when we were still hunters and foragers. We ran around and tried to eat as much as possible. Since you couldn't store food well for longer periods of time, you ate what you caught on a more or less day-to-day basis.
Carbs fill up our glycogen stores. As anyone who's gone keto while lifting can tell, your overall strength doesn't drop - but the number of reps drops drastically. Without carbs, easily accessible fuel (glycogen stored in the muscles) goes way down.
To a cave man, having fuel readily loaded in the muscles increased survivability. Having to wait for fat burning to fuel the body decreased survivability.
To get to my point - at last: Humans seek out sugar. This type of carbs taste good (and that's a result of evolution; we crave what increases survivability for our genes (cat's can't taste the sweetness)), and they serve a function: To enable us to exert power over time.
Grob, who had just eaten a tub of honey, could run farther than Brob, who had just eaten some eggs.
These days, this evolutionary pressure is no longer present. But our tastebuds have not adjusted, and they keep telling us to fill up on sugar and carbs - that we don't burn off, and so the body metabolism never gets around to burning fat. So it keeps accumulating.
But as Ossoi writes. When your BF is already low, and you keep active to burn off carbs, eating carbs is beneficial: It fuels longer, more effective work outs.