The reason for this is that Tampermonkey (and presumably others) do not actually diff the userscript from its source URL when checking for userscript updates -- rather, the userscript manager specifically checks for changes to that version string in the userscript metadata and will not update, even if you tell it to, unless the version differs. While it is possible to manually update by reinstalling the userscript, the user is never prompted to do so if the version does not change and reinstallation requires a few otherwise unnecessary extra steps.
If it isn't too much trouble, would you mind please incrementing the semantic version of the userscript (specifically, the version encoded here: https://github.com/cameroncondry/cbc-kitten-scientists/blob/master/kitten-scientists.user.js#L10) from time to time when you commit other updates?
The reason for this is that Tampermonkey (and presumably others) do not actually diff the userscript from its source URL when checking for userscript updates -- rather, the userscript manager specifically checks for changes to that version string in the userscript metadata and will not update, even if you tell it to, unless the version differs. While it is possible to manually update by reinstalling the userscript, the user is never prompted to do so if the version does not change and reinstallation requires a few otherwise unnecessary extra steps.