Maybe because it's "less risky"? Other than that, it may not be better ... if by "better" you mean more profitable. All depends on the statistics of strategy.
Risking 20% a trade will give you 5 chances to blow your account , risking 2 % will give you 50 chances , that is 45 more chances against market.
I'm just thinking of why one of by best strategies that I had where I turned 150$ to $300 in a week failed...I risked maybe 20% a trade and R:R was 1:1. 1 trade a day. But If I risked only 2% would it of been successful? I think maybe that the R:R would need to be better also in order for it to be successful or no?
Risk reward ratio of 1 to 1 is no good , as spreads will eventually eat up profits.When you catch a move , cut your losing trades and run your profits , it is those big winning moves which makes profitable traders .