The ending should be about resolving all the remaining plot threads and entering the stage of "rewarding the readers who have stuck with the series all this time." Since she doesn't understand what the readers actually want, she may have convinced herself that forcing in an NTR scene was a way of rewarding the people who had followed the series from the beginning. That might be the reason behind this entire mess.
But what's especially ironic is that if Katsura Airi actually listened to the readers right now, when their voices are practically unanimous about what they want, and had been able to restrain herself a little, this whole situation probably wouldn't have gone this far.