Kind of defeats the purpose of "bonus." I mean, it's literally the game's implementation of: "Oh, you logged in every day and did a quest? Good for you, here's a cookie."
It also gives players incentive to do roulettes daily. If tanks were like, 'eh, I will just do roulettes later in the week', then there would probably be a lot longer wait for DPS in the Roulette during the week.