There’s a difference between going from weekly to monthly and going from monthly to semi-annually. For one thing, (AIUI), it’s not good to have gas sitting in your car for more than a few months.
Also, it’s possible that during a given week you don’t go near a gas station (from where I live, if I hop on the freeway and head to the city, I don’t pass any). But it’s unlikely that if you drive for a month you’re not near a gas station at a convenient time to stop. So getting rid of the annoyance of weekly fill-ups is different from dealing with monthly fill-ups (which is not especially annoying).
Also, it’s possible that during a given week you don’t go near a gas station (from where I live, if I hop on the freeway and head to the city, I don’t pass any). But it’s unlikely that if you drive for a month you’re not near a gas station at a convenient time to stop. So getting rid of the annoyance of weekly fill-ups is different from dealing with monthly fill-ups (which is not especially annoying).