Because they used it as a tool to hunt down and arrest civil rights groups and Vietnam protestors.

Marijuana was considered a black person drug. If you didn't know, the US kinda hates black people, statistically speaking. It's pretty fucked up!

According to the available information, there is no direct mention of the percentage of black people who used marijuana in the 1960s and 1970s. However, we can infer some information from the provided snippets.
In the 1970s, marijuana use became more widespread among the general population. According to Gallup’s trend by age, widespread experimentation with marijuana first occurred among adults aged 18 to 29 between 1969 and 1973, rising from 8% to 35%. It then continued to mount, reaching 56% by 1977, and remained at that level in 1985.
It is important to note that the available information does not provide specific data on the percentage of black people who used marijuana during this time period. However, we can infer that marijuana use was more prevalent among younger adults, particularly those in the 18-29 age range, during the 1970s.
In terms of the potency of marijuana during this time period, reports suggest that pot in the 1970s had THC levels of around 1%. In contrast, today, the herb you’re smoking has a lot more THC, with levels averaging more than 6-8%. Some specially grown plants can contain THC levels as high as 51%.
It is also worth noting that a 2022 analysis of marijuana possession arrests in Texas for the years 2017 to 2019 reported that African Americans comprised 30.2 percent of all possession arrests, yet Black people comprised only 12.9 percent of the state’s population. This suggests that there may be racial disparities in marijuana use and arrest rates, but the available information does not provide specific data on the percentage of black people who used marijuana in the 1960s and 1970s.

Edit: The above is kind of incorrect, the herb I smoke brags ~25%, though sources say those #s vary greatly.

They tried banning alcohol. There was enough popular pushback they had no choice but to un-ban it.

There was less popular demand for marijuana. It seems like it's moving in the same direction, just more slowly.

What schedule do you think alcohol would be if it was illegal? 2?