It doesn't have built-in syncing, unlike KeePass. So if you want cloud syncing you have to install an entire syncer on your file system just for the sake of that one program. The assumption that everyone has or wants an automatic behind-the-scenes file syncer installed on every system they use the program on is quite a big and incorrect one.
No, the question is what if you do want cloud syncing for your passwords (you need to sync with your phone somehow without manually uploading/downloading from a browser every time...), but unable or unwilling to install a background cloud syncer installed on every system you use KeePassXC on. People blindly suggest KeePassXC without realizing not everyone has or wants a cloud syncer installed on their entire system.
> You're not really going to get around having to install "something" to sync your passwords if you want to have your passwords synced
Huh? This is obviously wrong; I'm doing literally this with KeePass. I haven't installed anything, and it has a plugin to sync directly with Google Drive that doesn't mess with or care about anything in the rest of the system.
Syncthing isn't very intrusive in my experience/opinion.
I created a keepass/syncthing directory somewhere inside my home directory, and I told Syncthing to sync only that directory. And the directory only contains the Keepass database plus a few Syncthing log files and such.