A wall chart works for one reason: you cannot avoid looking at it.
Twelve weeks, all visible at once. Mark a session and the row fills in. Miss a fortnight and the gap is right there at eye level — which is uncomfortable, and is precisely the mechanism.
Printed on heavy uncoated matte so a biro does not skid and a marker does not bleed through, and shipped flat rather than rolled, because a chart that will not lie against the wall gets put in a drawer.