He only did that after he finished his contract with Warner Brothers. Prince gave Warners a bunch of already recorded material he had in his vault and they made some albums from them: "Come", "Old Friends 4 Sale", "The Gold Experience", & "Chaos and Disorder". Warners had also put out the unreleased album from 1988 called "The Black Album" in 1994. Prince still had to fufill his contract. This is why he changed his name to the symbol and started writing "Slave" on his face. A contract is a legally binding document. You can't just break it, the record company can sue you. Peter Tork of The Monkees and Terence Trent D'arby had to buy out their contracts, which left them broke. Tori Amos wanted to leave Atlantic Records, but they wouldn't let her out of her contract and wouldn't promote or refuse to release material she returned to them. The artist has no power, the company does. The artist is just an employee. Invincble & HIStory didn't sell much in the US, only overseas. If you notice Michael never toured the USA after the Bad tour. Why is that?
are you saying the usa is the only country in the world? and, still, are you saying that between four and ten million copies is a failure? Michael did well in the usa. but, again, Michael did well around the world. using the usa, alone, is convenient, but not relevant. having said that, even two million in the usa, alone, is very good. and Michael did more than that. but, in the beginning, he did that. and that is good.
Michael used ingenuity, and therefore, had power. like i said...you can break a contract, without breaking a contract. Sony had to rerelease MJ's old material countless times, because MJ made new material very very sparse. that's a cool way to break a contract, without leaving a contract. and nothing that Sony tried, made MJ broke. if an artist has enough ingenuity, they can find ways to get out of a contract. you have power, unless you believe you don't.
perhaps those other artists, such as D'Arby, should have gone into publishing, like Michael. again...ceasing to write songs, is a clever way to not work for someone, anymore. whatever Warner did, with Prince, if anything, it made them want to release stuff from him, that they probably, otherwise would not have released. and, he could just sit back and do nothing. and then start over, when he got out of the contract, officially.