They're the cost of doing business under certain circumstances. Personally I think that weekend penalty rates and especially Sunday penalty rates need to be abolished outright. The Sunday penalty rate is a holdover of a much more observing Christian country that we no longer are. As a Mon-Fri worker there would be plenty of times I'd prefer to have a weekday off.
When it comes to it being the "cost of doing business" if that's the case then why shouldn't the specific extra costs fall upon those who cause the business to incur them instead of being socialised. If I get a coffee on a Tuesday morning then the cafe is incurring x staffing cost, on a Sunday they are incurring a 2x staffing cost. Why should I pay more for my coffee on a Tuesday so that you can get a coffee cheaper on a Sunday?
The crux of the surcharges is to pass on extra costs to those who incur them. You don't pay a card surcharge if you pay in cash, you don't pay a weekend surcharge if you shop when their staffing costs are lower.
Depends when their last increase to costs was though. Inflation's 4%, their staffing costs have gone up, their payment fees cannot be past on, their cost of materials has gone up considerably. I don't like paying more but you get to 10% pretty quickly. Years ago I worked for a food manufacturer and within the space of a year the tins that we packaged food into went up ~30%, just that made a notable increase in the cost of all of our goods.