My take is that most people don't see cannabis legalization as an important-enough issue. It's kind of "would be nice" issue that's overweighted by issues like economy, democracy, and immigration.
I'm not in the US, but that's my only explanation for why hasn't cannabis been legalized on the federal level yet, i.e. that people simply don't care enough about it to even be a part of the discussion.
The big divide is really by age. Older voters (in both parties) tend to oppose it. 72% of people under 30 are pro-legalization, but only 30% of people older than 75 are. The average for all US adults is 60%.
Younger voters' low turnout messes up the calculus here. But as soon as the number of young voters you'd gain exceeds the number of old voters a candidate would lose, you'll start to see this play out, and I think we're really close to that tipping point.
My comment is that making the 2024 election a referendum on legalization (and a few other big issues like abortion) will likely be the good strategic play. You could imagine a future, though, where they go ignore legalization and focus entirely on abortion and other issues.
But they would risk getting outflanked on legalization by a more libertarian-minded Republican, which could cost the election due to reducing turnout of young and disillusioned voters who would otherwise go Dem.