I think it's more than incompetence or accountability sinks; The DMV (and similar offices; Service {Canada, Ontario}, etc) are also the points at which the bureaucratic system of government interfaces with actual people as well. Boundary-layer components in any system are complicated because they have to distill complex input into abstractions understood by the system.
I recently emigrated to Canada from the States and exchanged my US state driver's license for one in my now-home province, but there were a ton of hoops to jump through to add my US driving history to my provincial record. The process seemed to be somewhat exceptional as the supervisor for the DMV-equivalent had to guide the reps I spoke to on how to append the multiple-states-of-history that I had to offer.
That's just a microcosm of what it wakes to distill the complexity of a person's life into pieces of verified information that a government can ingest. That's a lossy, complicated process that relies on both the 'customer' and the agent having a matching mutual understanding of what points of information can be agreed upon or, indeed, offered.
In some cases it's not clear, either; my wife was told initially that she would have to hand over her license from two states ago to update her history, because the province's documentation showed it was still active (despite the fact that our immediately-previous state merrily punched a big VOID hole in it, and that it was expired), but when she returned after digging up her voided license they said they didn't even need to see it. That last bit was possibly 'incompetence'; possibly on the part of the Canadian agency, for not being consistent on if they needed to see the license or not, or the US states, for not being up to date on their record keeping, but again: these are complex systems tryng to maintain consistency. It's reasonable to expect noise.