Being a Witness in Steemit block-chain is one of the most responsible work.
Because users Votes witnesses so that they will get assurence of security and stability in Steemit Block-chain.
There are 30 votes opportunities for every users to choose their 30 most trustworthy witness.

List is here:- https://steemit.com/~witnesses

It means we have opportunities to choose 30 witness out of 100+ witnesses. and they are keeping secure the Steemit Block-chain and they are responsible for growth of Steemit community.
We votes to witnesses because we have trust on them and they seems like active witness every time to keep secure and stable this Steemit Platform.
But If one or more witness went to offline for couple of days or more than that it means either he is not suitable for a witness or he is irresponsible.
And if there is any other reason for his availability, then his responsibility to check Every activity of black-chain, which were happened of his absence.

When I was checking the list of witnesses for voting i seen there that few witnesses are fired from the list..
@themarkymark, so the presence of witness in block-chain create trust on users that this specific black-chain based platform is Secure..