It's flexible and there are many storage options so just don't use Dropbox, if you don't trust it as well. Install Syncthing[1]. Or just use any SFTP-capable SSH server you have and can trust to hold the encrypted data. Or enable password-protected[2] WebDAV under some path on any of your nginx or Apache servers. Or set up Nextcloud.
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[1] If you use KeepassXC, it would be a little noisy about the lock files. I heard the plan is to just remove those (and always merge on save) as they don't serve their purpose any well. Same as with Dropbox, though.
[2] It could be also certificate-protected, but software support may vary.
1) They can't read your data.
2) They can see your favicons, but users like this feature. In Bitwarden, you can disable it.
3) Furthermore, Bitwarden is completely open source and you can decide on which cloud or server you want to host. Although using a good password is much more important.
Because in principle the files on Dropbox could just be dumped on the open internet -- Dropbox never sees anything unencrcypted. There is a lot more trust in a single tool.
LastPass says the same thing[1]
[1]https://www.lastpass.com/how-it-works
EDIT: No, I'm wrong. I was thinking in terms of login credentials (which neither are able to see); but LastPass does look at the URLs associated with your credentials so they can pull favicons