Terrible business model
Groupon might have made its founders (long gone) a fortune but the business was unsustainable. They hyper inflated into new territories screwing businesses left and right and leaving a barren wasteland of broken / burnt businesses behind them.
These days Groupon mostly sells crappy service deals - manicures, carpet cleaning etc. - where the business has low overheads and artificially inflates prices for a service to make the discount seem like a good deal. Not only that but there are dozens of rival coupon services selling similar deals. I'm surprised they've lasted as long as they have without imploding.