Kassandra’s curse isn’t, like, a supernatural one. I don’t know if that makes sense right off the bat, but let me explain myself: The curse isn’t that her prophecies are never believed, like. There’s no supernatural or divine force at play making people disbelieve her.
What Apollon did was give her such a grand gift of prophecy that her visions, when they come, are overwhelming and debilitating in their power. She’s exposed to the full force of divine prophecy with none of the blocks that most mortal prophets have---and not just that, but she full on knows the horror of the war, the siege, and the falling of Troy. And it’s a full-on sensory experience for Kassandra: past and future meld into the present and she lives it.
And so she screams her throat raw, she shouts from her windows, she pulls at her hair and sobs over a coming horror that no one else knows of.
No other prophet of Troy has her skill---not her brother, not the other priests of Apollon---and when they receive their prophecies and oracles, it’s not through visions. They read the weather, the birds, the bones, the innards of a sacrifice, etc. etc. Even if they have a clearer knowing than divination, they present their prophecies and oracles in a very calm and detached manner.
You don’t---you don’t see them screaming their prophecies in the middle of the marketplace.
It’s crazy people shit. People don’t believe Kassandra because she’s freaking out over what’s happened/will happen/is happening and no one fucking believes her because they just see a crazy lady screaming.