It's definitely becoming more and more prevalent as time goes on, due to more and more methods available online to gamble with and more sites with little or no verification required to deposit and withdraw. There's two sides to crypto-based gambling, and this is the darker side.

As for CS:GO Skins and items associated with gambling there, I believe everything really started with the concept of cases to unlock skins, starting sometime in 2013, and gambling with virtual skins really began to grow around that. There's definitely some actions being taken by Valve to stop this, including cases being locked with no option to unlock in Belgium and the Netherlands, as well as the regular banning of gambling site bots to stop sites from operating, though.