It makes you wonder what OP uses his coupons if he is saying lucky dice is, in general, a bad event for f2ps. Opposite to what he thinks and someone already said this, it's a good event f2ps to spend. If you only spend only on RNG events so you hope to get a ninja, then you have no right to judge if you don't know how to effectively use your coupons.

^Pretty much sums it up. Since the majority of f2ps aren't like OP, they still need power items (or at least see value after spending their coupons) in lucky dice and will look at this event worth spending.