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That's because every witness does a job of their own. The main responsibility is keeping the blockchain running, but most have side projects.
There's a column URL on https://steemd.com/witnesses where every witness can put a description.

Oh, k, so my experience running other blockchains means I could just as easily be a witness should I be able to get the votes. K.

You can "be a witness" here for the cost of a cloud vps. Being a visible, profitable, witness with votes enough to even get to a break even position is a whole nother matter entirely.

You may have experience in POW chains, but what experience do you have with dPOS chains?