The point of advertising Lost in Spain is that two channels have the rights for it: Cuatro, a general network, and Fox, which here is a cable channel and shows it a day or two before.

Therefore, Cuatro needs to advertise Lost to make sure that people watch it a day after many other people!

Wow, good point, there's barely any advertising for this final season here in the US. But then again, why spend millions to advertise a show that has an existing fanbase and doesn't need to increase it since it's the final season.