There is no real legal, moral or scientific reason why the age restriction in the state marijuana legalization initiatives should be 21 instead of 19 or 22, but it is a political necessity.

The American people overwhelmingly want the drinking age to remain 21. According to a new Gallup poll, 74 percent would oppose a federal law lowering the drinking age to 18 across the country. It found every major political subgroup opposes this change. From Gallup:

Favor or Oppose Lowering Drinking Age to 18

Given that the American public is still relatively skeptical about the idea of legal marijuana there is no way they would support making marijuana more readily available than alcohol.

While there might be some good arguments for why the United States should bring its drinking age more in line with those in Europe, that is separate debate the American people don’t seem very open to at the moment.

With only a modest majority of voters in support of the idea of marijuana legalization, ballot initiative campaigns can’t afford to alienate voters with an unpopular provision that takes the losing side on this age topic.

In Uruguay it was possible to set the legal age for marijuana purchasing at 18 because they don’t have a higher drinking age, but that won’t work politically in the United States.

For whatever reason Americans have decided they really like an age limit of 21, so that is why all three legalization initiative this year, Oregon, Alaska, and Washington D.C., needed to go with that number.

Jon Walker is the author of After Legalization: Understanding the future of marijuana policy