Harry Styles doesn't have another hit on his album and it was obvious since may. Not commercial songs at all. And Kiwi is the most rock song on the album. What did you expect from it? The performance on Xfactor was lit, totally. He rocked the stage. But it is just not the song that a lot of people will buy. This song is not going anywhere, but performances with it will be amazing. Harry's singles look like complete flops but still helping him to sell his album without being hits on spotify, iTunes and radio. In streaming era it's hard.
And Liam Payne went to top 20 only because his song was already #28 on Itunes before xfactor. Kiwi was not even in top 200 before the show.
And well, now kiwi is #39, the album is #13. Harry just keep selling his album and gaining new fans after every promo he is doing. He is doing more than just fine.