Original: One reason for the controversy is that whilst the scheme has been lucrative for its private-sector operator, Capita, some critics argue it has failed to raise the promised levels of funding for public transport as costs eat up the revenue.
Simplified: One reason for the controversy is that whilst the scheme has been lucrative for its private-sector operator, Capita, some people argue it has not made enough money for public transport because the money has been spent on other things.