“Definitely, once a week,” is easier than “sometimes,” and “daily” is easier than once a week.
A daily ritual keeps something front-of-mind, makes it almost automatic, ensures that whatever else happens, a small step gets made. Once the pattern is established, you don’t need to think about it – the decision has already been made.
Weekly rituals are a bit harder – you need cues to help you make sure you don’t miss the date, and the consequences of missing the commitment are longer lasting because the next chance for catching up might be seven days from now.
Monthly rituals are harder still – “third Sunday of the month” is too lengthy a formula.
It seems to me that the less regular a commitment is, the more people and resources you need to involve to make sure it happens. This is why we have no problem remembering to celebrate Christmas or the New Year: we reinforce the rituals by reminding each other, and we don’t want to let the others down.*
*We also invest in these events in advance, paying deposits in the form of preparations made, gifts bought, tickets and bookings made in advance.