The whole point is that those records did exist and were active. Who is responsible for the integrity of the database? Who audits it? Why didn't they see it? Why didn't they fix it.
When I worked in industry, I was responsible for many databases, either inherited or self-made. With the inherited ones, the first thing I did was check the plausibility of the data, then the integrity. In all cases, the data was wildly incorrect, so my first task was to sort it out.
One would expect Government departments to have procedures for auditing and quality control departments to keep the databases accurate, unless there was an instruction or guideline to stop that. It's not laziness, nor incompetence. Musk's team found it on day one, and they don't even work there. I suspect that the reason they checked is because they are suspicious about postal votes. All you need for a postal vote is a national insurance number and an address. Audits already showed that addresses were fake.
Did you know that 43% of George Galloway's votes in the Rochdale bi-election were postal. That compares with a 4% average, which used to be about 0.05% pre-covid. I also heard that in the last general election, David Lammy, Angela Rayner, Rachel from accounts and Jess Phillips all had a substantially disproportionate number of postal votes compared with other MPs.