The whole mood of the vrata is that it’s about Kṛṣṇa, but here it’s just all about their inconvenience of fasting. So better they not fast. They will get more spiritual benefit.
Dvaraka was not a village, neither was Indraprastha, neither was Mathura, neither was Hastinapura. So Varnashrama also includes cities. The main point is Krishna consciousness.