So you saw a product that (1) gives you complete control of your data (2) uses an open format (3) only charges for sync, publish, and commercial use, and you thought to yourself:

"What a great use of my time building a competitor that adds no value, just to save a few dollars a month on sync and publishing. I hope other people value their time as little as I do and contribute"

Have fun!

But Obsidian doesn't even require a few dollars a month for sync. You can use Github or whatever sync service you want. Your data is just a directory of markdown files. That said, I've paid for the sync service for years, but only because it works really well on Linux. I've always been impressed with Obsidian's first-class Linux offerings.

it's nice to have open source implementations so you can extend / borrow / merge / morph features and ideas into something else