The reason "wickedness continues to our day" is supposedly because Satan challenged God saying he could turn all mankind away from him so God needed to prove to his creation once and for all times that they couldn't manage without him. Then when things started taking shape, he brought the flood and wiped them all out, just to have it start all over again.
God isn't slow respecting his promises but wants all to attain righteousness. The longer he waits, the more people the JW's can save. Yet more and more people are being born every day that are obviously not paying any heed to JW's.