Outside this bubble, rsync and git and cron are not solutions to syncing your files across devices. Outside this bubble, people just want a solution to the problem, not a box of parts to construct their own solution to the problem from 2nd principles.
…Also, people tend to want this inside the bubble too :-)
https://slack.com/app-pages/google-calendar
This is not robust cross-platform syncing of huge files on flaky networks. This is looking for the the word "dog" in your calendar and changing the emoji to a dog.
The user you replied to is (I assume) suggesting someone else can make a recreation of the service and give it away. i.e. not suggesting everyone hack together their own implementation
It strikes me that there's a positive correlation between executive pay, and the user-hostility of the resulting product. Firefox (and derivatives) is my daily driver, but I despise the company that makes it. They made their name by being a lightweight, standards-compliant fast browser. I don't know how the company became such a pile of sh*, but I find it credible that excessive executive pay has more than a little to do with it.
It's one thing to implement something. It's another thing to implement it in a way that makes other people want to use it.