Why not a pull request?
1. The original word2vec is considered a reference implementation, used for benchmarks, so some people might not want it to change much.
2. The original hasn't been updated since 2017, and development was never very interactive.
3. word2vec has been widely reimplemented, and some reimplementations may be more widely used than the original (particularly Gensim).
4. The original had a paper from the very start (rather than being an open source project where a paper came later), so other papers reference it. For future papers that use the koan form, having a paper makes it easy to use in a similar way.