Presumably your journey history is always recorded but as an inducement to
avoid paying commission to small shops etc TfL prefer you pay them direct
and offer this carrot.

I've always assumed it was because the online Oyster ticketing is outsourced
to Keith Prowse (or somebody like that) and it wouldn't be appropriate to
give your journey history to a company you've never been a customer of. I
suspect I am completely wrong though :-)