The 'authorities' don't do it; it's up to individual practices, who spend a vast amount of time & energy on mailouts, text messages and ringing round, as well as reminders to callers in person or by phone and on prescription repeats, on top of promotion inside and (in our case) outside the surgery. We still only get the same folk year after year generally.
FF, if you're in a target group, your GP is letting youdown badly, and letting him/herself down, too, as there is (a small amount of0 money attached to flu jabs.