While I appreciate the sentiment behind this, with experience comes a sixth sense of what should be rebuilt, and what is better reused/modified. Experience also brings with it an ability to scan through foreign code and get a "feel" for how usable it is.
For example, I've chosen to replace one of the foundational data communication building blocks [1] because, after extensive research, the existing systems can't be modified to handle all of the general use cases I want handled. And it won't stop there, because I also have a number of additional requirements that HTTP won't handle (so there's also a new protocol in the works that will be based off this technology). If I could have simply modified an existing system to do what I want, I certainly wouldn't have spent the last two years on this! I've got plenty of other things demanding my attention...
For example, I've chosen to replace one of the foundational data communication building blocks [1] because, after extensive research, the existing systems can't be modified to handle all of the general use cases I want handled. And it won't stop there, because I also have a number of additional requirements that HTTP won't handle (so there's also a new protocol in the works that will be based off this technology). If I could have simply modified an existing system to do what I want, I certainly wouldn't have spent the last two years on this! I've got plenty of other things demanding my attention...
[1] https://concise-encoding.org