Growing up I would go to the bookstore, buy a book, read it, then have to wait a year to find out what happened next. It's how it was, it was expected. Series would almost always have a cliffhanger at the end of each book, except for the final one. That was life. Then self publishing happened, and for a while, everything carried on as normal. As authors started publishing on their own schedule instead of the once a year schedule of most publishing houses, books and series released faster and faster. Then readers started complaining about cliffhangers. Saying things like they’ll refuse to read a book or series if there is one. Ummmm what? Cliffhangers have always been a part of publishing. Especially series. If you read a series and it isn’t billed as a series of stand alones, you can probably expect to find a cliffhanger in there. Before I go further, let’s go over what a cliffhanger is, and isn’t. A cliffhanger is a story that ends at a sometimes (suspenseful) part of the story that leads into the following book. It will wrap up the current books story arc but NOT the series arc. (That gets carried over.) What a cliffhanger isn’t, is a book that ends at a random point and does not conclude that particular books story arc without wrapping anything up. Now, it’s not always easy to pick out an individual story arc vs the series story arc unless you’re familiar with those elements. That’s okay. It can take some time to learn those things. Wanting to know what happens next and having to wait can suck. But it’s a part of storytelling that has been around for ages. Cliffhangers make good sense. It brings readers back once the next book is out with more urgency than if a story is just wrapped up. Not all stories can be told in a single volume. And that is why we have series. I have heard cliffhangers called reader abuse and emotional manipulation. It’s not holding anyone hostage. A good cliffhanger will have you turning the last page and wanting the next book right away. It’s a hook. That’s what hooks do. Cliffhangers are an element of storytelling that has been around for ages. Writers want readers to be emotionally invested in their series so they read the entire story and discover the whole world, and the entire journey they’ve spent months and months and sometimes even years crafting. Growing up being indie wasn’t a thing, so when books came out you often had to wait a year for the next installment and it was normal to have cliffhangers if it was a series. (It is still overwhelmingly the norm.) Just because there is a cliffhanger does not mean that the story arc for that book wasn’t resolved, but that the start of a new arc has been introduced at the end of that book so readers who are invested in the book and love it will also have a little extra incentive to want to go and pick up the next book. It’s not a trend, it’s not a cheap trick. It’s a valid part of storytelling. And like it or not, writing (the same goes for TV shows and movies and any form of entertainment) is a business. People will always want readers/watchers/etc to return. To be honest, and this might piss a few people off… I think throwing a fit and refusing to read the remainder of a series is a childish reaction and smacks of entitlement. Would you have continued on if there wasn’t a cliffhanger? If not, then don’t blame the cliffhanger. If yes, then that is just a petty tantrum in believing you deserve everything you want the second you decide you want it. It’s one thing to not like a book enough to continue a series—it happens. That’s okay.
But it’s another mindset all together to be spiteful because someone is trying to make a living doing a thing that has been around for the history of storytelling, for trying to do something they love and makes them happy, that makes others happy and brings them hours of joy and entertainment.
Really, by refusing to read a book or series that has a cliffhanger, the only one you're hurting is yourself by depriving yourself of amazing stories and beautiful and fantastic worlds.
It's okay to wait until the series is out, but keep in mind many authors gauge intrest in their series by sale and preorders, so buy the books when they come out and use that as a way to let the author know you want them to finish the series. Because if not enough people buy, then the author might give up and move on to another series.