Scammers don't need this to copy an existing website, and I could see plenty of legitimate uses. Maybe you're redoing the website but want to keep the previous site around somewhere, or you want an easy way to archive a site for future reference. Maybe you're tired of paying for some hosted CMS but you want to keep the content.
The website in question may be a dynamic website (e.g., WordPress, MediaWiki, or whatever other CMS or custom web app) and you either want a snapshot of it for backup, or you run it locally and want un static copy to host it elsewhere that only support static files.
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Scammers don't need this to copy an existing website, and I could see plenty of legitimate uses. Maybe you're redoing the website but want to keep the previous site around somewhere, or you want an easy way to archive a site for future reference. Maybe you're tired of paying for some hosted CMS but you want to keep the content.
All the scenarios you described can be achieved by having access to the source code, assuming you own it.
Lots of things are possible with access to source code that are still easier when someone writes a tool for that scenario.
Crawling a build you already have isn't one of them
The website in question may be a dynamic website (e.g., WordPress, MediaWiki, or whatever other CMS or custom web app) and you either want a snapshot of it for backup, or you run it locally and want un static copy to host it elsewhere that only support static files.