One of the reasons is that after you scrape it you want to do something with the data: put it in a Postgres/SQLite, save it to disk, POST it to some webserver,

One of the reasons is that after you scrape it you want to do something with the data: put it in a Postgres/SQLite, save it to disk, POST it to some webserver, extract some stats from it and write to a CSV, ... This stuff is much easier to do in Python.