First, your described software still has versions. Each daily snapshot or git commit or whatever is a new version. There's no reason you can't put an auto-incrementing version number on each release and call that your version number. You can even stick a "0." on the front of it and be SemVer complant.

Second, just because some people do this doesn't mean it's a good idea. If you're writing a full application and just want to distribute it, do whatever you want with your versioning (although using a dependency management tool to distribute your webapp or CLI tool is probably not a great idea in the first place), but if you are writing something to be included in another project please use a sane versioning system. Anything else is selfish and disrespectful of your users.