That's totally possible. There is definitely a potential timeline where it just gets basically ignored.

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.

What your percentages don't say is how many pro-legalization want it bad enough for it to matter more than other issues when considering their vote.

Part of the problem is that for most people the subject of legalizing cannabis is considered only in the context of "more people are going to use drugs". It needs to be framed in how much it costs society to enforce those laws (both in money and freedom).