Name, address and contact details are recorded as well. Primarily so that, should you need to apply for a duplicate, the TOC can find you in the database given most people can't/don't remember their photocard number.
I understand why the TOC you acquired your photocard from would know that, but I don't understand why it needs to be made centrally available?
You have to know your railcard number to buy a season ticket from a TVM anyway.
The duplicate point is reasonably valid, but I'm sure there could be a way of a TOC requesting that information or even something like saying that only National Rail operated stations can process duplicates for tickets not purchased from the photocard-originating TOC.
I suppose the real reason why nobody has done such a thing is because not many people move around very often so it isn't really a problem
In fact - why aren't season photocards managed by ATOC in the same way as Railcards?