There's too much risk involved to run a publishing company entirely by business world rules. A publisher can write a business plan and prepare a mission statement, but no one can predict whether a book will sell or not until it's in front of the public. Small press started because there was a new breed of poets and writers in the 1950's and 60's who had something to say that wasn't supported by the existing publishing houses. Poets began publishing their own and other writer's books. They found they enjoyed the creative freedom of publishing whatever they wanted whenever they wanted.
People still get into small press because they have something to say.
They pay for the privilege themselves and take the risk, and hope it pays off. From Jenkins' list, I get the impression he thinks publishing is a full time job for small press people. That would be nice, but for most small publishers this is, as D'Avalon said, a part time job. I don't know many people who are able to publish without working 40 hours a week at a regular job. The fact is, the only people who can afford to publish full time are those that publish how-to and resources for other publishers.