There are many reasons why people can’t or won’t get state IDs, even if you can’t fathom it. Until we have mandatory federal IDs (which, incidentally, Republicans are usually against because...facism or something), making them required for a civic duty is just dumb and unfair.
But...uhm, what if you don't have your birth certificate lying around somewhere? What if its like California, you have to pay $50 and wait in line for a few hours? Or what if you try to get a state ID and they want a utility bill to pay your residence?
There are billions of little things.
You can do a lot without an ID card. You can even fly with evidence of identity that doesn't require an ID. You can actually bank as long as you know your SS# and can provide another form of identity (e.g. birth certificate). You might not be able to get a credit card, but those are rich people problems.
Anyways, there is an entire world that you and I are not very familiar with.