In just about every mass-market book I've read over the last couple of months (at least, the recently published books), I have seen formula kick into gear in the first chapter. Why?
There are two possible reasons:
(a) Formula sells.
(b) Agents and editors think that formula sells.
These days, I think it's going to be hard for anyone to get an agent and a publisher if they aren't willing to make at least some concessions to formula. I know that in my own acquisitions, I am running about 50/50: half formula, half breakout.
It is tempting to dismiss formula as "bad." It is not. In the right hands, it can be done very well. In the wrong hands, reading it feels as though you're reading a book-by-the-numbers, where the author has simply dropped in character and place names.
What, then, does Formula mean? This isn't going to be a detailed description, but rather how I think about the definition of the term.
Primarily, Formula serves two functions: It gives readers an easy entry into the story and it keeps the story going until the end.
Formula does NOT do a few things. It does NOT challenge readers. It does NOT lead to an unhappy (or even an unresolved) ending. It does NOT ask readers to think subtly. It does NOT offer gradations of emotion. While good Formula is well written, it does not have any aspirations for its language other than to tell a good story and entertain the reader.
Ultimately, Formula comes down to a single idea: "This is what readers want and expect. I'm going to give it to them."
Formula generally means motivating characters through a few common channels, often combined: SICKNESS, DEATH, LOVERS, and CHILDREN. If you think about it, there are no more powerful motivators. Nothing elicits sympathy/empathy like a sick child or the death of a lover (or, sick lover or dead child). Save the child - save the lover - Protect the child from harm - protect the lover from harm - and there's your plot, right there.
You may wonder why so many protagonists have dead spouses and/or sick or estranged children. There's your answer.
Formula then means erecting barriers to the protagonist's achieving his or her main goal of child or lover protection. Protagonist jumps through hoops on his/her way to defeating the Bad Guy.
If it all sounds quite Hollywood, well, it is. I do think we are seeing a sort of leveling in story-telling across the media in which books, films, TV shows, etc., follow the same formula. (Maybe not so much in plays, though I could be wrong about that.) I carefully read Amazon and Goodreads review of books I have published that go against strict formula (I do the same for non-formulaic books that I have NOT published). In the most critical reader reviews, there's often a common denominator: The book did something the reader didn't like or agree with. What these readers are often saying, without saying it directly, is that the book violated formula. It interfered with their expectations and they didn't like that.
This is why I come back to something I've said before and will say many times before I die: The best books end up with about a 3-star average. In many ways, a 3-star rating is more of a badge of honor than a 5-star rating. One of the most provocative reads of the last few years was Adam Ross's MR. PEANUT: 3 stars on Amazon as of this writing. Take a look at the Amazon page for Gillian Flynn's GONE GIRL: a 4-star average, but thousands of 1-, 2-, and 3-star reviews. That was a book that took chances and succeeded beautifully. But look at the number of people who complain about the unresolved ending (anti-formula), the lack of immediately likable characters (anti-formula), the dueling narrators (anti-formula). Also note how ANGRY so many of these reviewers feel about key elements of formula being withheld from them, and you begin to understand why agents and publishers are so afraid to take a chance on anything that doesn't walk a very straight formulaic line.