Good Question. The STEEM blockchain is opensource and run by the witnesses. Anyone can operate a steem blockchain or smoke blockchain witness node. The top witnesses make money for keeping the network afloat. The smoke.io witness is easy to set up with docker. It is a heck of a lot of fun to do if you're into computers.
Here is my post about how I set my smoke.io witness up.
https://smoke.io/life/@hightimes/how-i-set-up-a-smoke-io-witness-hotbox-on-digital-ocean-with-ubuntu-bionic-20-step-guide

Also you can vote for your witnesses here:
https://steemitwallet.com/~witnesses

Heres some more info about steemit witnesses here:
https://steemit.com/witness-category/@jerrybanfield/steem-witness-basic-training