So What's With All The Boot Camps In Military Fiction?

I’m reading Brad Torgerson’s The Chaplain’s War right now, which is currently half of a helluva book.
The opening half had a start that dragged me right in – huge, mechano-mantis creatures had effortlessly destroyed our invading armada, and a handful of prisoners were trapped on an alien planet.  The chaplain’s assistant, who is not particularly religious but is the only man left to comfort these POWs after the chaplain was killed in battle, is approached by one of the mantis-overlords: they’ve decided to exterminate humanity, but first they want to try to understand this foolish concept humans have called “God.”
Problem is, the chaplain’s assistant isn’t quite sure he understands it.  But he does understand that teaching them something is the only hope humanity has.
Things don’t go quite where you expected from there.
The problem is that this narrative has serious drive – the stakes are great, there’s huge battles, there’s desperate moves from needy people on both sides.  I can’t wait to see what happens next…
…but unfortunately, at least thus far in the book (I’m about a quarter of the way through), every other chapter is a flashback to the chaplain at bootcamp.
There’s a lot of bootcamp narratives in military fiction.  And I feel, at this point, like I’ve seen most of them.  The recruit arrives at the boot camp as saggy sack of potatoes.  The upper echelons insult them gratuitously, give them impossible tasks and then punish them for not doing it.  Because we can’t demean the officers, there is of course a local villain – either a slacker who’s going to take other good soldiers out with him, or a nasty piece of work who has it in for Our Hero, or both.  And eventually, Our Hero learns more responsibility and camaraderie and becomes tougher than he’s ever been before.
It’s a lot like the Cop Narrative, in that I feel I’ve seen it too many times to get excited about it.  And I love it when there are twists – I think Ender’s Game did a great job in twisting it so that the boot camp created isolation and not brotherhood, I think Old Man’s War had the joy of seeing elderly people given new genetically engineered bodies lusting for a second life, and The Forever War had a boot camp in icy space that was almost more fatal than the war.
Yet I keep seeing that boot camp narrative show up in novels without much of a twist, and I wonder: what’s appealing about it?
I thought initially it was that soldiers love to relive that time period and will read anything that triggers that experience, and maybe it is, but I posted a status update yesterday and three ex-military friends of mine expressed the same bafflement.  I suspect I may be friended to outliers, but still.
And I myself am an outlier myself in that I don’t comfort-read.  I know there are people who read, say, romances merely because they’re predictable, taking comfort in hearing all the narrative tropes click into place, and I’m not one of them.  (People keep saying my novel Flex is wildly unpredictable, and that’s because if I got bored when I was writing it I tore up that chapter and wrote something weirder.)  So maybe it’s that military fiction readers like having variants on the same story, and they’d get itchy if the boot camp didn’t make its obligatory appearance.
And Brad’s a smart writer.  By alternating boot camp with ZOMG MANTIS WARS, he’s telling me implicitly that the audience he’s trying to court would find both halves equally compelling.  I don’t.  For me, it’s kind of like “These chapters are about an eight-year-old boy trying to fight off his murderous stepfather with a steak knife, and these alternating chapters are about his friend’s struggle to fix his ant farm.” I’m all like WTF MANTIS and find myself skimming the boot camp chapters like blazes to GET TO THE BUGS.
And maybe the boot camp pays off.  It may be a narrative choice to have something with the boot camp resound firmly down the pike – again, Brad’s smart, I wouldn’t put that off of him.  But I’ve seen so many fictional boot camps that don’t really pay off at this stage that I find myself wondering where the appeal of boot camp in general stems from.  There’s nothing wrong with it, I’m just trying to figure it out.
Any ideas?