Colin Rosenstiel wrote:

Why should I be expected to get an Oyster for just 7 single tube fares
so far this year?

Nobody *expects* you to do anything, but you are offered a choice. You
can freely choose an oyster which will bring you a certain type of
convenience along with a cheaper cost of travel, or you can freely
choose not to get one, which will relieve you of the tiresome burden of
planning ahead and remembering to carry it with you, and will only cost
you a few quid more than the oyster price.

--
http://gallery120232.fotopic.net/p9632973.html
(43 140 nearing completion at Crewe Works in 1979)