@TheLarkInn asked, and it seems like a discussion worth having.

Leaving it off by default would lead to people being more likely to get errors in things like Node by default, but it would potentially make the workflow easier for people using Webpack, since it's usually easier to add additional plugins than it is to remove them, since opting out first is more verbose, so people could do

{
  presets: ['@babel/env'],
  env: {
    test: {
      plugins: ['@babel/transform-modules-commonjs'],
    }
  }
}

which is a lot nicer than

{
  presets: [['@babel/env', { modules: false }]],
  env: {
    test: {
      plugins: ['@babel/transform-modules-commonjs'],
    }
  }
}

or even

{
  presets: [['@babel/env', { modules: false }]],
  env: {
    test: {
      presets: ['@babel/env'],
    }
  }
}

at least in my view?