Shops are quiet on weekdays.
閑散としている（かんさんとしている）is a better collocation with 商店街 than ひっそりしている in this context.
- 閑散とした means “quiet” and “idle/sluggish” (business operation). That means in this 商店街 (shopping district) context that there are few customers on weekdays.
- ひっそりとしている means that there are actually customers in the shopping district, but they try not to make a noise.