You can tell parcel generate an analysis of what is in your bundle by adding --reporter @parcel/reporter-bundle-analyzer to your parcel build command, which will output an html file with the analysis to the parcel-bundle-reports folder (see docs). That analysis will at least tell you what is the main contributor(s) to the bundle size are.

Parcel does try to remove unused code from your bundle through scope hoisting and tree-shaking (see docs), but there are things that can mess up this process. You can get additional information about whether and why parcel might have had trouble here by adding the --log-level verbose flag to your parcel build command.