RC's are a perpetual arms race, thanks to the war on drugs. Any time one draws enough attention to itself, it tends to get added to the list of banned compounds. Afterwards, typically between 1 and 3 new ones are designed by chemists (usually in China) and hit the market.
RC's typically draw attention to themselves in one of two ways.

1. Some idiot ingests/insufflates one without bothering to research dosage or potential drug interactions and bad things happen as a result.
2. Some drug dealer sells an RC as something it isn't, such as 25x-NBOMe's being sold as LSD, or cathinones being sold as MDMA.

The second possibility is by far the worst of the two. In the case of NBOMe's being sold as LSD, LSD is (physically) safe in high dosages - as high as 10-25 hits. NBOMe's on the other hand (25b- in particular) can be lethal at such dosages. Virtually anytime you hear about someone dying from LSD or MDMA at a festival, you can be sure they never took the actual drug that their death is attributed to. People who knowingly and intentionally mislabel their wares to make them more attractive are literally death dealers.

As far as the laws go, here in the US, the majority of RC's are technically banned by default, thanks to the Analogue Act. The Analog Act essentially states that if you package up and distribute a chemical that is an analog of a banned compound, as far as the law is concerned that is the same as selling the banned compound.
The law's legal foundation and constitutionality are questionable at best, but due to how the Federal court system is rigged here, it's unlikely to actually get challenged, since the vast majority of cases end in plea-bargains.