They don't have inventory/consumables which makes money laundering easier. The low transaction cost makes paying cash normal. The primary cost is labor and they force the indentured employees to pay it back for 'living expenses'.

Nail salons make a lot of money. manicures and pedicures cost a lot, depending on the class level they might be $50-$500. Supplies cost almost nothing. The workers are usually immigrants making very little living in communal housing.

Cheap to patronize, low barrier to entry, and can’t be done over the internet.

Same in other European countries, usually the rumors are they take advantage of business sponsorship activities, or some kind of money laundry, taxes evasion.

My guess would be that for middle class people, it's a simple luxury that is considered worth stretching for and reasonably easy to budget around.

Incredibly low capex and opex so once you've got it running you can basically just throttle the business in accordance with demand.

Laundry.

Logistics. They tend to act as the maul for unethical products.

Glasgow at one point had eight American Candy Stores that were always empty but been operational for years. Not even good American Candy.