Why would people buy STEEM?
Over and above the speculation naturally present, theres a much more transcendental reason why people buy STEEM, whereby they not only benefit from speculative gains, but they also play an active role in shaping the future of their investment.
Considering the fact that anyone can become a whale and influence and support Steemits content by curating, the answer why many buy STEEM is obviously to power up. 
For those who are critical about what theyre seeing on Steemit and want to see something different, you have the opportunity to stop your complaining and act positively by buying STEEM, powering up, and making your ideas heard (best done to begin with in my opinion by actively curating).
What Steemit is and what it will be is in the hands of the community, and many people buy STEEM to join in, take part of and shape that community.
And the door is open to all.