One of the main reasons is that the spread of scam is used as a result of the manipulation,goverment can not control the transactions, used in illegal activity and the government thinks it affects the country's economy but it is not the reason
i think by giving strict regulations to ico, it will filter out the quality, so competition will be healthy, and not many investors will be deceived, i think that is a good first step.
Governments should come up solutions for this ICO's otherwise, many people who don't know about the blockchain are launching the ICO and scamming the people. So it is always good to have rules and regulation for launching any ICO.