@JagiThePretender, there is increased demand because hard forks mean you either get the new token for free, or, like in this case, they bring an update to the cryptocurrency itself. Whether or not the update/new token is worth the buzz is always uncertain in these situations, but rallies in the market are not always logical. Just look at Long Island Iced Tea --> Long Blockchain, for example.
@JagiThePretender, because they know nothing about forthcoming hardfork. They think that it will be free coins, but in reality, SC forthcoming hardfork just will fix a block time generation. Siacoin's forthcoming hardfork absolutely will not affect the price.