Bitcoin can't just be bought up like Steemit did, it's a completely decentralized protocol.
The only thing that could happen is a massive corporation or government sinks a load of money into Bitcoin mining equipment to perform a majority attack.
That said, even if somebody tries to attack the network for a takeover, a chain split will just isolate those miners anyway. In short, Bitcoin is too big to become centralized now.
but there is a big difference here. when someone controls majority of a coin like steem they can control everything from transactions to forks and code changes since they have full control but in bitcoin even if someone had a very large percentage of the hashrate they still can't control the network. all they could do is mine empty blocks to create a big backlog otherwise if they make any changes it will be rejected by the entire network.