There are a number of reasons that a website could be worth as little as that. For example, let say the website earned a $1000 monthly profit, but requires the website operator to invest 200-300 hours of labor per month to achieve that level of profit. If you add in the cost of labor, then it isn’t really making money, and a buyer is only purchasing the “potential” to make money.
There are other possible hidden cost issues, and there is also the occasional “stupid” person that simply cannot substantiate their profits.