The chemical in cannabis is THC. It can produce sensory and psychological effects. And this is why we feel "high" when we smoke marijuana.
In the US, cannabis laws are passed state by state. As of 2019 it is illegal at the federal level and many people complain about draconian sentencing in parts of the country!
Many would-be activists are reluctant to put their jobs and reputation on the line to publicly advocate for cannabis law reform. The pressure to conform to the status quo can be even greater in politically conservate locales.