I, like Daniel, am genuinely interested to know.


My reason for using the online top-up facility was to gain online access
to my journey history.

That seems still to be a requirement. From the Oyster site:

"You need to have an Oyster online account and have purchased pay as you
go online to view your journey history online. Once you are logged in,
select the Journey History option under the 'My card' tab."

That may of course simply change the question to why online top-up is
required. I'd guess as a security check (with DPA in mind) that the
person gaining access is the owner of the card. Not foolproof of course
but it seems to me a reasonable safeguard.

--
R