Why do you need to validate citizenship when issuing a voter ID if citizenship was already validated when registering to vote? That seems like a completely redundant requirement that is only put in place to make it slightly more difficult to acquire said ID.

I don't think citizenship is actually validated when you register to vote. I live in California and all I had to do was go on their website and check a couple boxes and fill out a form.

In several areas it is permissible for residents to be registered to vote in municipal elections etc. In some places, the local government has made efforts to get those who are neither legal residents not citizens registered for local elections. In those locations, enforcing a requirement to validate citizenship when availing onesself of the privileges thereof (e.g. voting in federal elections) makes sense.