it doesn't need to because it gets enough funding to cover expenses. Twitter already has ads and it can always add more. Given the huge userbase & growth the potential is unlimited.
I have the POTENTIAL to be POTUS (Just ask my mom if you dont believe me!), but unless I get off my ass and start making contacts, get involved in the right political causes etc it does not mean shit.
When my mortgage is due if I go to the banker and say "I don't have any money, but I have a shit load of traffic on my new fancy pants web 2.0 site" how far do you think I get with him?
you're comparing apples and oranges. If someone gave you 30M you would have no difficulty paying the mortgage.