Why? First, it keeps practice consistent--we don't call Hamas the Islamic Resistance because we use their acronym in Arabic Daesh apparently is the acronym if we use the Arabic name.
Second, it is insulting to them since daesh has other meanings:
Daesh sounds similar to the Arabic words Daes ("one who crushes something underfoot") and Dahes ("one who sows discord")Third, I feel bad for all of the girls named ISIS and all of the Institutes with this acronym.
But mostly, we should use it because it pisses off those who belong to Daesh.