Even though skin gambling might be viewed differently: it depends on who are you asking. Some people might view it negatively as it changes how the skins are valued, some will say that this is a great way to get a bit more skins or money.
The reason why the sites like Drakelounge are up and running is because of Valve. This is the company which created the Steam API, which allows logging into the gambling websites with your Steam ID. If the API would be disabled and websites could now allow logging in with Steam ID, then this kind of gambling would not be able to take place.
So in a sense, the whole betting area is controlled by the company who created CSGO in the first place. Of course, that means that they can make various conditions that these websites will have to follow. There were some instances where Valve demanded to get a license: if the website could not provide one, they would get banned (the API would not work for them).
When skin gambling started, it was mostly limited to CSGO, but these days you can even bet with skins from other games.
It might be weird that the company does not close such websites, but if they are trusted (like Drakelounge), Valve allows them to continue as they believe skins will not get real monetary value