Genuinely not hard to understand the difference between legalization and decriminalization:

Decriminalization: criminal punishment is removed from an activity

Legalization: legislation is enacted to regulate an activity

The reason the Black and brown communities that were traditionally involved in the drug trade have not majorly benefited from pro-marijuana legislation is because the bulk of it has been legalization that enacted new rules about who can legally sell, not decriminalization.

If we’d decriminalized marijuana then the people who’d historically made a living selling it would be able to keep on doing that, but without fear of the police.

But we didn’t, and as a result, many of them are still criminalized because they can’t afford to participate in the legal system and thus sell their wares on the black market.

Granted, there are some consumer benefits to legalization: those rules and regulations are partly intended to make sure that the cannabis you’re sold is safe to consume. But it comes at a very specific cost.