A yearly call can carry continuity through months that had little to say.

Some relationships do not need frequency, they need one reliable point of contact. A call that happens every year at roughly the same time holds the thread, and the eleven silent months are not neglect but the shape of that particular friendship. Trouble comes from measuring every relationship on one scale. Continuity can be carried by very little, provided the very little actually happens.

Think of somebody you are fond of and rarely speak to, and put one annual contact in the calendar. Making it recur means it survives the years when neither of you would have got round to it.