Not super relevant for lodash in particular, but another reason for why someone might want to do this is dependency hell. At least with code you write yourself,

Not super relevant for lodash in particular, but another reason for why someone might want to do this is dependency hell. At least with code you write yourself, you know that the author(s) won't keep changing the API (very common in the javascript ecosystem, unfortunately), forcing you to either waste time constantly changing your own code to match the newer APIs, or stick to a single version for a long time, which may become incompatible with newer versions of other dependencies, your build system, your language, your environment, etc, which will become an issue if you have something else that you want to update but that old version of the dependency doesn't support it. So in some cases it might be easier and more maintainable to just write your own version of whatever small feature of the dependency you might otherwise have used, but knowing when this will be the case is a skill of its own.