Before epilepsy was understood to be a neurological condition, people believed it was caused by the moon, or by phlegm in the brain. They condemned seizures as evidence of witchcraft or demonic possession, and killed or castrated sufferers to prevent them from passing tainted blood to a new generation.
But if we’re admitting a fixed trajectory through spacetime to the present based on a multitude of parameters with fixed values (nothing would change because we changed nothing), then we are excluding randomness. So assuming no randomness, why would those parameters evolve in an unpredictable fashion (i.e. choice, unhindered by ‘external’ factors) and cause an unknowable trajectory through spacetime from the present to the future? I admit it’s unlikely to be able to calculate said trajectory with current knowledge and technology though.
I argue that randomness is excluded because it does not exist. I question how there could be choice unhindered by external factors. Where in our universe does true randomness exist? If we had two exact copies of the universe, and in both a die was dropped in the exact universe state down to the atoms of the brain, hand, table, cube, wind, etc., it would be the same result, no?
The fact that a dice roll is unknowable doesn’t mean it was any less determined by the variety of factors that led up to it.
You ask why parameters would evolve in an unknowable fashion. That is simply because the universe is complex and there are so many unmeasurable parameters as you mentioned. No technology or knowledge could ever measure the state of all subatomic particles instantaneously. We aren’t talking about a comparitovrly simple computer program that you can run twice and just get the same result. There are so many parameters that there is perhaps no number large enough to define it.