The struggle to suspend disbelief

This week I've been slogging my way through a young adult fantasy novel.  It's written by an author whose earlier work I enjoyed immensely, but this time round I wasn't engaged by the story.  I've been feeling that more and more with fantasy books recently, and I've been trying to work out why this is.  Why is it that I can't suspend my disbelief, leave it at the door of the story, and get engaged in that world?

I think one reason with modern fantasy novels is their authors' determination to work issues from our modern world, like diversity and gender fluidity, into their stories.  Sometimes these #ownvoices are clunky additions to the storyline.  What the author has done is insert present-day politics and sensitivities into their, essentially, historically-based story.  But  the trouble is, often these additions feel false. They pay lip service to our current culture, rather than being a seamless part of the culture that author is writing about.  That might, of course, be driven by the publisher rather than the author.

I have less of a problem with magical realism. Julie Kagawa's Talon series, about dragons who can shapeshift into humans, I found convincing and enjoyable, but her series putting a modern-day girl into the world of the fae I couldn't engage with.

Similarly, another author's work which has a broadly medieval-level society based around a giant travelling fair also didn't engage me.  I did read to the end of that book, but only to try and work out why so many people raved about it.  I still hadn't figured that out when I reached the end.

That author had a viewpoint character, a boy working as a gay prostitute.  The book contained an explicit scene of the boy having sex with a client.  To me, this just felt like the author saying "Look!  Not only women can sell their bodies.  Men do it too."  And to me, that felt like a strident attempt to impose modern-day discussions on a medieval fantasy world.

In the last few years I've veered sharply towards reading science fiction rather than fantasy.  But here's the thing: I have no trouble accepting sentient, talking bamboo, or the awakening to full awareness of bioengineered dogs.  Or bioengineered sentient spiders.  Some of these stories border on fantasy, but they work for me.  And they work for other readers too, they're all well-regarded books.

Often, I think, what drives suspension of disbelief for me is centred more around what the characters do rather than who they are.  If the fight of good against evil is one I can accept on a moral basis, then maybe I'm more willing to suspend my disbelief in a ridiculous story.  So basically I want the sentient bamboo, dogs, or spiders, to be on the "right" side.  

This still gets nowhere near being the whole answer to the question, but it's a start.