Unfortunately this seems to be the case; lockfiles would be unnecessary only if all your dependencies (and their dependencies, recursively all the way down) reference explicit versions, the risk being that a new malicious version would be published. I'll research if there's a workaround.

Thanks everyone for pointing out this issue.

Thread hypothesis is that we want to avoid breakage due to automatic dependency updates. So, don't update dependencies automatically. Now sure, if you tell the tool to update a particular dep, it will force second- and higher-order deps to update to compatible versions. It will always use the oldest compatible version, so nothing will get broken in surprising fashion. This seems strange to people who've used mostly npm and node, but tools for other languages have this policy.