I know that rollup in particular is intended to collect all your JS modules, somewhat like an .a file in your filesystem, but Webpack can easily combine all the assets.

In both cases you’re downloading globs of stuff that could already be in your cache, or that you don’t want to download at all (e.g. ads). I have never approved of efforts to turn the web into a “TV remote with a ‘Buy’ button” (which stretches back decades) but indeed, I consider such projects pernicious.