OAbot historically does not remove anything from the "url" parameter because it was thought that this would make it easier to eventually make its operations automatic on the English Wikipedia. We're currently not trying to get the bot account to edit URLs, so we can at least make life easier for users who manually use the tool.
This is more necessary now that Citation bot stopped removing certain redundant URLs by publishers even when they're closed access. We can no longer rely on Citation bot to clean up the mess left behind by VisualEditor/Citoid on thousands of articles (T232771).
Moreover, some users' interpretations of the outcome of the recent RfC on Auto-linking titles in citations of works with free-to-read DOIs go in the direction of an increased addition of links in the URL parameter, so OAbot should help users wishing to do that.
When removing an existing URL it's necessary to also remove all the related parameters like access-date, url-status, archive-url, archive-date etc. Sometimes they can be very messy.