Why do we need a decentralized mining operation? I know people use decentralization to prevent attacks from hackers and governments that are trying to take it down. Is this one of the motivations behind a decentralized mining operation or is this more about decentralized decision making powers?

It could also mean that decentralized mining operations might prevent a 51% attack, if the mining pools are more decentralized. Right?

Please expand a bit more on the concept and what the motivation for this was.