Basically we don't know the risk in every site if you invest money in a site first is you don't know if the site was trusted there are site that can give you small profit but many site are just scamming people who invested.
Yes that is why investment is consider as too risky because you doesn't have sureness that it will success. If you want to invest your money make sure first that the site is trusted and has a good background.
What you are telling is the basic thing which every investors have to know about it before going for investing, but in my point why to invest bitcoin in other investment when bitcoin purchasing and storing itself is a big investment as you can see the price of bitcoin how it is moving.