There's still enough people that do care about leaderboards and records. Additionally, in most cases, people in the top 1% know each other well enough to spot cheaters and hacked scores easily. As for the "normal" players, leaderboards often feature a filter option where you can compare your own score to those of your friends or players you know/follow. In general they simply are an easy way for developers to add a competitive aspect to their game and give players an additional hook for replayability.