£50k you do not get family benefit but if both parents earn £49k each they are eligible

Law changed a few years ago that if you earn over £50k you are not entitled to family benefit. If this law changed it should not change for people already claiming just like tax credits. What about all the others, including the very rich? Is this really fair to actually take money off people who were originally entitled. 50k is not a rich income and especially for a one income family with several children. Laws should change for future newcomers.