Instagram send secret spies to ban your account as selling it is against nearly every sites terms Lol.
Yeah some stars are useless considering the staff aren't full downies but they need proof that they are selling the account so if you star it out than the missing word can be anything.
Many users are fragile about some pixels well.. I can't say much as I have my shop starred up to fuck but it's to stop the companies from banning that specific username.
Like everybody else said.
Accounts (Twitches, Tumblrs and Gamertags mostly) have been banned due to being sold as it's against the TOS or the company doesn't like it. People star out their items in order to minimize the risk.