So I read a fair bit of fantasy in various flavours and as such I tend to see the same tropes over and over, because, well because that's tropes for you really, but sometimes this bugs me and one of those sometimes is prophecy. There are a number of reasons for this.
Problem one: Why are prophecies so often in the form of really bad poetry? two reasons probably, firstly, that's what Nostradamus's prophecies look like and secondly because bad poetry is really good for hiding what you meant and thus requiring an explanation later on and also, importantly, not completely spoiling the plot. The first reason I don't object to, but the second gets on my nerves, though admittedly for quite a pretentious reason. The thing is I strongly believe that poetry should add to comprehension not take away from it. Ideally, a poetic description of a person / place / event should convey a strong sense of who / what / etc you're talking about in just a few words, the choice of one synonym rather than another should convey extra information about the subject (and not just declare that you have a vocabulary and aren't afraid to use it), good poetry is memorable and conveys emotion and so forth. Obviously here I'm mostly talking lyrical prose rather than actual rhyming couplets or whatever which have a whole bunch of extra constraints to wrestle with, but yeah, I get annoyed by poetry being deliberately used to obscure things.
Problem two: Why are prophecies always true? All right, it's fantasy, there are a number of possible reasons why a prophecy might be true (mostly coming down to magic, gods, predestination or some combination thereof) but in worlds where there are a large number of people acting, basically, like people why aren't there also reams and reams of false prophecy that are devoutly believed in? (credit where it's due, some authors do this and then prophecy becomes way more awesome as a device). Also, all too often a prophecy in a low fantasy setting where there's a lack of sufficiently powerful magic / beings to explain how the prophecy could possibly be made to be true will still have a true prophecy for no good reason.
Problem three: Why do some writers use prophecy as really lazy foreshadowing? Obvious answer, because it's easy, look I phrased the first two problems as questions then had to do the same with this one and it didn't quite work, just deal with it. I think my issue with this is actually broader than using prophecy as foreshadowing, it's more about clunky foreshadowing in general, that feeling I get sometimes when I'm reading that the author is saying 'yeah I know this bit is a kinda dull, but look there's awesome stuff coming up, keep reading'. It's bearable when the author is wrong and actually 'this bit' is not as dull as all that, but honestly, have a little faith, you don't have to put a bit at the end of every chapter that says 'and in the next chapter things get worse' I know that, if it's a book and you managed to get it published then every single chapter with the possible exception of the last one is probably going to be a rendition of 'and it got worse' either trust me to keep reading, or be a little less obvious with the pleas for attention.