Why the hate? It's a genuine question. When you rewrite something, you need to justify the effort somehow. The GNU coreutils started out as "the BSD utilities, but with the GPL!".
Because the reimplementation authors skip all the complexities of designing the tool in the first place while getting right to the fun part (which is coding), and then they get to call themselves authors of a well known infrastructure tool.
Compare "I have typed a setuid() wrapper in rust" vs "I'm the author of sudo-rs".
Compare "I have typed a setuid() wrapper in rust" vs "I'm the author of sudo-rs".