In his own reddit AskMeEverything page,
https://www.reddit.com/r/IAmA/comments/80ow6w/im_bill_gates_cochair_of_the_bill_melinda_gates/He answers about cryptocurrency stating
The main feature of crypto currencies is their anonymity. I don't think this is a good thing. The Governments ability to find money laundering and tax evasion and terrorist funding is a good thing. Right now crypto currencies are used for buying fentanyl and other drugs so it is a rare technology that has caused deaths in a fairly direct way. I think the speculative wave around ICOs and crypto currencies is super risky for those who go long.
He isn't wrong in his sense, if the cryptocurrency is to have a future, they should be able to create an environment of trust between themselves and the authorities.
Firstly, We have to think and realize that Bill gates is a tycoon businessman in the entire world. We don't know what He is thinking, and one of the factor He most thinking about is to think rich more, meaning It may have a probability one of his strategy to earn more, since He knows to himself that He has the capacity to influence others, this maybe reason. Of course once the market get down, this could be His chance to buy a huge of cryptocurrecny that has a potentials to increase its value in the future. But this is just only assessment.