Pretty basic idea here.  A criminal is someone who commits a crime.  A crime is violation of a specific criminal statute.  There are requirements imposed by law that are not criminal.

Failure to register your vehicle is actually a civil requirement.  In Colorado, failure to register can result in a late fee of up to $100.  Operating a vehicle with expired registration is an infraction, not a crime.  You can't be jailed for driving with expired tags.