It may not be realistic but it's efficient in terms of time and production budget. Designing new clothes for the character require a new character sheet/turnaround for each character for the sake of consistency and you're not just drawing the front view, you'll have to draw the side, 3/4 view and back view as well and that will consume more time ESPECIALLY if you have like 10+ characters in your series. Imagine if you have to design new armors/costumes for every 10 characters to wear each day.
It's okay if your setting is the real world then it's easier to change their outfit. But if it's a fantasy setting, you can get away by not changing their outfit all the time since it's focuses more on the characters having their own signature or trademark design.
On a side note, my comic is a mixture of real world and fantasy so my human characters change outfits every now and then and it's easy because they wear real life clothing (shirts, jeans, shorts, etc.) that don't require me to create turnarounds of them all the time. The angels on the other hand, wears fantasy costume not to mention they have their own signature outfit which is more difficult to change and WILL require me to create new sets of turnarounds and that will consume more time. Also, I can get away with it since they're spirits they won't get stinky or anything like that.