We all heard of “bread and circuses”, which is a way to distract the masses to keep them pacified and not bring down the system controlled by the elite. In this case idols would be included in the circus part.
You’ll also notice that the government will use popular idols for certain types of PR (RV in North Korea, EXO meeting Trump, BTS getting kudos from Korean gov). So while idols don’t start as “tools” they can become one if they have a large following. As long as they keep their audiences focused on things not related to the power structure they’ll get deals + support from the governments and large corporate interests.