Working with systems long term teaches you that the value of a system is not about the theoretical efficiency but rather the practical efficiency, and this has facets during all phases of a system lifetime. For example, rapid implementation may often trump correctness, comprehensibility of ease of delegation/handover/hiring may often trump other concerns, and reliability / longevity are often facets that come to the fore over time.
Re-inventing the wheel can actually be a great strategy then, if you plan on keeping something around for a long time, especially if in doing so you (a) document it; (b) fully understand it; (c) remain free of external dependencies.