It looks like raindrop is a for-profit company which does not publish source code under a free license, or at least i could not find it on the homepage. In comparison, wallabag is fully free software: you can self-host it, or you can have a commercial contract with the maintainers to host it for you. In both cases, you can donate money for development.

The main developer publishes regularly about the finances of the project and the economic sustainability of free-software. The last update was only available in french though: https://nicolas.loeuillet.org/billets/2022/01/03/wallabagit-...

To be fair, wallabag is also mostly maintained by a single person. However, there's a wide community so it's unlikely the software would go unmaintained if a bus accident occurred. I must admit i have no idea about the "hosted" side of things and if the maintainer has a backup plan for someone to take over in case they're not available.