Nice! My "longer" commute is about the same, 22km (because I'm only 4km from my workplace so the longer commute is for fitness, physical and mental) and I'll try to ride that every day during good weather.

I find my mental state really improves with a ride in to work so I try to ride as often as possible which is close to 4x/wk from June to September. Last April, for the #30DaysOfBiking, I rode 26 days and last June for the Canadian Cycling Challenge, I commuted every work day and at least one day on the weekends (and rode a touch over 1,000km that month).

Riding every day is not necessary for everyone but some, because they don't have a car or are short on funds, use those as motivation. You do not need to ride every day unless you find a reason to do so, including the challenge of trying to do so. But other reasons may motivate you to ride every day or at least try. I'll avoid active thunder storms. You know how you count after a lightning strike until you hear thunder to see how far away it is, 5 seconds = 1 mile, well one day, I was riding home during a warm summer rain when there were 3 lightning strikes about 3-4 minutes apart, the thunder sounded 7 seconds after the first strike, 3 seconds after the second, and after the third, I didn't even count 1 when the thunder sounded, I was inspired to speed up!!

Do what you're motivated to do but certainly don't consider it a requirement to be a part of this group (or even the car-free group, some of whom I'm sure take alternate modes of transportation at times).