Marijuana probably could pass. They didn’t really try. It’s supported by most Republican voters. It’d be a death sentence for a lot of the Republicans to vote against it.
It helps maintain the status quo though, so they didn’t want it gone.
Again requires Congressional action and there have been multiple bills that have passed through a democratic controlled house or Senate but stalled in the other half of Congress because Republicans wouldn’t vote for it and there wasn’t a large enough majority of Dems to get it done. Go check out mpp.org for more info. It doesn’t take but 10-15 minutes of looking up information to find out Dems attempted to get it done but once again Republican obstruction (like has been happening since 2008) prevented real reforms.