Collecting and storing DNA is a tricky thing because there is a fine line between the right to privacy and protecting the general population criminally speaking. I know it varies from state to state as to what can be collected and stored and for what purpose. Then you look at things like the tens of thousands of untested rape kits backlogged out there, so it's not a black or white situation.
Again DNA aside, the bigger question with IY in AB's car is the lack of fingerprints. We know those are in the system because he has been arrested so many times. The fact they were not able to identify him through fingerprints is puzzling because, like you, I don't believe he was walking around with gloves, or smart enough to think of it. IY seems unpredictable and not the seasoned criminal who thinks about leaving fingerprints behind. This whole crime was sloppy from start to finish. Even him taking her at the gas station, which everyone knows is usually filled with cameras, was messy and not thought out.