I can understand Bitcoin: it's a decentralized, permission-less system to store and transfer value. If you want to use that storage and value transfer system, then you obviously need to store some of your own value into that system. So you buy BTC and you drive the price up ever so slightly.
But why would anyone buy STEEM? You don't need more than your 10 starting STEEM to post, comment or read stuff on steemit.
The only reason to own STEEM that I can see is to get even more STEEM by posting and curating content. If the price of STEEM remained steady or increased, that would be good enough.
However, there is a 100% yearly inflation. Assuming the market cap remains constant, that means each STEEM will lose half of its value by next year. That is a tremendous downward pressure: why would anybody invest into something that loses half of its value every year? Unless the market cap increases, but that brings us back to the first point: why would anybody buy STEEM with USD or any other fiat?
There is also another risk: even if you buy STEEM and power them up, you might end up losing more money to inflation than you will make from contributing on steemit, if you are a less popular than average contributor.
I really cannot figure out the economic model of STEEM.
If nobody has a good reason to buy STEEM, then the currently rising price is a bubble resulting from pure speculation. What is going to happen 2 years from now, when huge volumes of STEEM have been powered down and nobody is there to buy it?