You don't really get any benefit from writing it in javascript, other than the normal benefits you get from writing anything in javascript. (I say this having very little experience with server-side javascript, so take it with a grain of salt)

DoM emulation and selectors are pretty much equivalent between nodejs and python, you can use css or xpath selectors on html/xml content on either of them. Either way you need to emulate something like a DoM, as neither language/execution-environment has a "native" DoM.

You don't want to execute random javascript code from the web inside your scraper, and just being able to parse the scripts doesn't do you much good. So you're not getting the main advantage I think you're suggesting, being able to emulate page javascript, being able to actually run that code.

Generally if you want to interact with javascript you need to do it in another process (I guess a sufficiently advanced sandbox could work too, an interpreter in your interpreter, but so far that doesn't exist). If you're already going to be running that javascript in a different process for security reasons that different process might as well just be a "remote controlled" web browser.

Historically that was done using selenium, which has good python bindings.

Now days it's being done more with playwright, which started out as a nodejs binding but is moving towards python....

Ultimately I think the reason is that there's no real advantage to using javascript and python is a nicer language with a healthier ecosystem, but your mileage my vary.