It looks like a research station that was designed to be _maintained_ on Earth. Their sense of cleanliness, I feel, is going to cost them in labor and repairability in the long run.
So many integrated panels. A microwave? Plants out in the work area with no shielding and nothing to constrain waste from floating away?
Pretty cowboy lookin' up there.
I do not see why you find this surprising.
There exists no better method for heating the food there, and many kinds of food are much tastier and also healthier warm than cold. They might eat some paste from a tube, but it certainly becomes more appetizing if it is heated.
The cost of having there microwave ovens is low and the improvement in the quality of the food is great. Moreover, they might also be useful for heating water or other things for some of the scientific experiments.
It also looks like they have a conventional ISS-style "suitcase" warmer, and a hot and cold water dispenser similar to the ISS. I expect the microwave is used sparingly.