Because it's a scam and you can lose a lot of money, that's one way to look at it, the other angle is, all the rich people, just want Bitcoin to die already, so they invest in all different medias to criticize bitcoin, so they can buy it cheaper than before, and after that sell it as much as they can at higher prices. So will we let them to have all the bitcoins??
There are people who criticize and there are also people who support the use of Bitcoin. This depends on the perception and how the person thinks. Usually everyone has their own goals and that is what distinguishes each opinion. For me it is better to support the use of Bitcoin because the more sophisticated the times will require us all to reach a much more sophisticated level of life such as the digitization of the financial system.