I remember a time when I was on smaller "cult hit" books like SHE-HULK and GREAT LAKES AVENGERS and I complained to the powers-that-be that my books weren't being promoted enough. Everywhere I looked the house ads and other forms of promotion were going to the big books like AVENGERS, AMAZING SPIDER-MAN, and the big events. I argued that if more of that promotion went to smaller titles, Marvel would see a better return because those smaller titles would benefit from that exposure so much more than titles that were already guaranteed hits. Their line of argument went the opposite way-- that the bigger titles brought in more far more revenue and that those were the titles that you had to keep a greater spotlight on with their promotional ads.
I was also told that I was no different from the writers on those big books-- because they TOO were complaining that they weren't getting enough promotion. And I was told that one day, if I was on one of those kinds of titles, that I would still feel the same way. That stuck with me. Years later, when the promotional materials were coming out for SPIDER-ISLAND, I made a point of going to the powers-that-be to tell them, "Y'know what? I'll say it. I AM getting too much promotion." (They also understood that, yes, I was being a smart ass.)
I'm no mind reader. I can't tell you how or why (or by how much) each book is promoted the way it is. But I can tell you this much: Marvel is a company. Marvel always wants the answer that will make them the most money. And Marvel *hates* to waste money. They would never do anything to willfully sabotage a comic that they were spending good money on. They never want ANY book to perform poorly. They would never hire a writer, penciler, inker, or colorist for a book they somehow "wanted to fail". They would never want to damage their relationships with those creators. They would never want to waste that editorial office's time on such a counterproductive endeavor.