How come they do that? Don't the 'worse students' need more scaling
The best students should be the ones who receive more scaling. If you do very well in a subject where everyone does well, you should benefit from that. If you do poorly in a subject where everyone does poorly, you shouldn't receive any benefits - your marks need to reflect your position in the subject and your position in the state.
Scaling isn't designed to bring poor performers up to the standards of good performers. Scaling is to ensure the good performers aren't penalised by putting in more effort and gaining highers marks. This is why students are strongly recommended to do subjects they like and are likely to do well in.