With tabs, the bar management has to do risk management: to decide who is allowed to keep a tab and how large each tab can get. This is hard to do without access to customers financial data. With credit cards, that risk management is done by the credit card network (mainly the issuer bank). The merchant pays a fee, and in return it gets cash at a predictable timeline with relatively little risk.
https://en.wikipedia.org/wiki/Diners_Club_International#Orig...
With tabs, the bar management has to do risk management: to decide who is allowed to keep a tab and how large each tab can get. This is hard to do without access to customers financial data. With credit cards, that risk management is done by the credit card network (mainly the issuer bank). The merchant pays a fee, and in return it gets cash at a predictable timeline with relatively little risk.