This isn't trivial when you start syncing mobile (now you need an extra app, as onedrive doesn't support local), or onto a work device (where I don't want onedrive installed)
There's work arounds (for example I forgot the name, but one plugin allows you to setup onedrive to share just one folder via logging in on each device), but the syncing story wasn't great. Quite a bit of extra setup across all devices, more points of failure etc.
Hence the smart business model, of let us handle it for you for a small cost.
There's an Obisidian plugin for direct syncing to OneDrive that works on both mobile and desktop - this keeps you from having to deal with either triggered syncs through github or the various other, painful syncing processes.
There's work arounds (for example I forgot the name, but one plugin allows you to setup onedrive to share just one folder via logging in on each device), but the syncing story wasn't great. Quite a bit of extra setup across all devices, more points of failure etc.
Hence the smart business model, of let us handle it for you for a small cost.