Because it is an ill thought of tax. Any tax that is signed into law must at least be broadly fair. If the Government could not be asked to design a law appropriately then they shouldn't collect this tax. The HMRC taxes those families with a single person earning £50,000 and above, but leaves families with couples earning £49,999 each . I feel this tax was allowed to pass because it was just easier to convince the electorate that these "rich people"(earning £50,000 and above should pay more ) instead of designing an appropriate tax. 