> If someone is running everyday like this, do they actually even need to lose weight? Aren't they already very fit?

Not necessarily. There's a reason the saying is "You can't outrun a bad diet."

Before I got my diet dialed in I was cycling every day, upwards of 10 miles a day with a couple 20 mile rides per week, and was still gaining weight because I ate like crap, and more importantly, still ate more than I was burning with all the exercise.

The average American consumes 3,864 calories per day. A moderately active male might have a maintenance of ~2,647 calories, give or take a couple hundred. Just eating 500 calories per day over what you burn will lead to about a 1lb increase in weight per week. A zone 2 run might burn somewhere between 500-600 calories per hour, so its easy to see how quickly over eating can add up and at a point it becomes basically impossible to "run it off."

There's other factors that play into it such as lean mass vs. fat, etc. but in general, you can be very active and still be overweight.

I understand what you are saying but OP is not an average American. They have been running every single day for 10 years, so chances of them already being very conscious about their diet are very high I think.