Ask HN: Why there are so many broken links on tech blogs?

When I read the blog from tech companies like Twitter and Github. I found lots of links are 404. For instance, on page https://github.blog/2018-06-20-mysql-high-availability-at-github/, there are three broken links

1.https://github.com/openark/orchestrator/blob/primary/docs/pseudo-gtid.md

2.https://github.com/openark/orchestrator/blob/primary/docs/raft.md

3.https://github.com/openark/orchestrator/blob/primary/docs/failure-detection.md

Why they didn't use some tools like deadlinkchecker to monitor their blogs and fix the links?