All fiat currencies can be speculative assets. Why bitcoin can't? There is a whole financial market called Forex, which is based on fiat currency trading pairs such as USD/EUR
The short answer is, fiat currencies are purposefully inflationary
The long answer is that Bitcoin has been made deflationary, due to a hard cap, coin loss, hoarding, or whatever. In the view of Gresham's Law, Bitcoin is good money to be stashed away, while fiat is bad money to be spent shortly. So whenever there is a choice to be made between what to spend and what to save, the choice is evident and straightforward, so there is no need to name it here
The reward distribution is basically a fee paid for a service (securing the network, through mining). The incentive will last only a few decades, which will also generated new coins and properly distribute them alogn the years
At first glance it kinda makes sense
I mean a fee for a service and that stuff. However, when you think about it, a currency of and in itself is purely utilitarian, and as such it works better when you have to pay for it. And aside from the block reward, the miners are also collecting transaction fees, and these are no going anywhere, at least as long as Bitcoin itself stays with us, alive and kicking