Reimplementing the functionality of existing and free software libraries provides a boost to learning when trying to become a better programmer. Usually, it's pointless and a waste of time.
Netflix and other large, online companies do it, because they fight for millisecond speed improvements, handle millions of requests per second, achieve uptime of over 99.99% and reuse the same source code in hundreds of places. Netflix still uses libraries from other companies wherever their quality is sufficient.
Software is hard to make. People spend countless hours on it. Appreciate that and reuse as much of their work as possible. Don't reimplement.