Accompanying ML/AI (and computer science, in general) papers with the relevant code is much desirable, both for reproducibility of the paper results as well as for faster integration of these results into applications.
Some researchers do so by themselves; but this has lately become also a community job, where a third, independent individual or team, not affiliated with the paper author(s), offers a code implementation starting from the paper.
A good, very recent case is the reproduction of the World Models paper (blog post, Github repo). Many of the implementations available at Papers with Code are indeed provided by the community.
A great write-up of such an effort, containing many lessons learned, made big raves recently: Lessons Learned Reproducing a Deep Reinforcement Learning Paper.
Understandably, individuals that have such efforts in their CV are a good recruiting option...