I didn't say that. I think it's dismissed more because the majority of marketing campaigns send out a dishonest message, and because of that customers are getting more and more insensitive to such campaigns.
And I also don't think it is an engineering process in the traditional way (although it's fashionable for everything that has a feedback loop to be called engineering these days). Marketing is more about social interactions, being more inline with humanities / social sciences ... and it takes a certain kind of skill-set to be good at it, and I've seen too few technical people being good at it.
Think of marketing as the social component of design. You wouldn't start coding an application before you had at least a rough design of what its functionality would be, right? So why would you start designing a product before you identified who is going to use it and what they will be using it for? Marketing answers those questions.
In rough, marketing identifies your market: Who will be using your product and why. Your application / business is then built using that knowledge.