Anecdotal but I was never asked to register to vote at my local DMV or from anyone else in life. I even come from a very political family and willingly chose to register to vote when I got my drivers license at 18.
Are they
supposed to ask? I know they have to give you the opportunity at DMVs due to federal law, but I'm not sure if they are required to actually ask you. I know I was never asked here in Florida. It's also not that uncommon for state motor vehicle agencies to have been sued to force compliance with these laws - Nevada, Connecticut and Texas were in the past couple years and had to change up their procedures. Georgia's recent adoption of automatic voter registration was due to a lawsuit about non-compliance as well, irrc.
FWIW, California voter laws now are very liberal. Same-day + auto reg, pre-registration for 16 & 17 year olds and ample registration opportunities for students. I don't really think there is anything more they can do, short of doing away with voter registration altogether a la North Dakota.