They think it proves loyalty. NetRatings also tracks this activity. Where new users can sign up. Wall Street analysts track this number. Smart investors often try to guesstimate this figure.
Most Internet companies trumpet one or the other.
Ultimately it doesn't matter if you get lots of customers unless you can also make money from them. Right now, it loses on every customer. The more customers, the more it loses. Likewise, it doesn't matter if you make money from every visitor unless you also have lots of visitors. Ultimately, the stock market will regain its sanity.