Some of them don't think it's a racial slur - that's the point.
We could, I suppose, get into a long discussion of how many or what percentage of people need to be offended before a remark is defined as a slur. However the DC football team has had its name for a long time, and I find it somewhat unconvincing that the name is now a major problem. Having said that, it is obviously not my opinion that should decide the issue.
If the team needs to change its name, then I propose that the cost of the change be divided throughout every team in the NFL, and each team can figure out how to come up with the funds.