As usual, follow the money
"primary purpose of the cards was still not clear"
Not true at all. The primary purpose of ID cards is the transfer of billions of pounds out of the pockets of the people and into the pockets of "the usual suspects" within the IT industry.
There can be no other explanation for the billions of pounds wasted on failed government computer projects. No entity can be so bad at learning the simple lesson. If you don't know what you want, how can you ever decide how to build it? (This has been highlighted in every NAO report on the subject.) Cockup or conspiracy? As usual, follow the money. Why do the same few IT companies keep winning huge government IT project contracts despite all of them having a long history of failure?
One of the unspoken rules of hiring an IT consultant is that you must first have a pretty good idea of what the correct answer must look like. Otherwise, how can you judge the quality of the answer? Sadly, it seems that the government is clueless about technology and apparently believes every single word they pay so much to hear.