First, to leave someone in a job fit that is not good is a disservice to the individual involved. Almost always a poor job fit also means the individual involved is not happy or fulfilled. At some level they probably know the fit is not right and while they may not want to confront it for reasons of job security we don't do them a favor by allowing them to stay in a place that does not fit them. As one leader said to me recently about a staff member who needed to move along, "She won't like it in the short run but a year from now she will thank me for doing it." We are stewards of others and as such we need to act when necessary.
Second. When there is not a good job fit, others are impacted! Other team members are always negatively impacted by an individual who is not a good fit for their job. To ignore the issue is to disempower the rest of the team. Saving ourselves the discomfort of a potentially difficult conversation leaves other staff having to deal with the poor fit of one of their colleagues. As stewards we cannot do that.
Third, our own leadership credibility is at stake when we ignore these issues. When leaders ignore known issues they lose credibility with their staff who are also aware of those issues. Staff have a right to expect their leaders to have the best interests of the team in mind and to act accordingly. If we ignore issues out of our own discomfort we lose credibility with our staff.