In the first place, Taylor has withdrawn. He submitted the paperwork about 45 minutes before the deadline. In the second place, why do they have to pick a replacement?
Another article today: he gave an invalid reason to withdraw, so they put him back on the ballot. If he is allowed to withdraw, the party is required to replace him because this is after the primary.
It's a silly little thing called State Law. Withdrawal is covered by one statute, replacement is covered by another. Many states have similar laws designed to prevent some of the gamesmanship that we are seeing on parade in this race.
You are correct, Taylor has withdrawn, but because he failed to comply with the requirements of the law before the deadline for withdrawal, his name will remain on the ballot and most of Wyandotte County will vote for him.