Same reason most songs flops later on in the era. It's old. Didn't it peak at like #17? Songs usually peak when they're popular/new. Sure, videos re-spark some interest, but fans have had this song on repeat for over a year now. They want new material.
fans don't buy post album singles. It's flopping because the GP isn't interested in OOTW.
Right? Plus people trying it with those re-release singles. If "1989" was released with new material you know damn well it would be guaranteed Hot 100 top 10. Laughable tries.
Personally I don't like it but I think everyone who was interested already has it, from the album when it was on iTunes before the album release, I think it was in the top 5 or something
So Wildest Dreams could go Top 10 after the music video once 1989 sold 5m+ copies but now that 1989 is at 5.5m (only 500k more than when WD was selling) OOTW can't even break the Top 40? The song just isn't clicking. Get over it, 5 hits is good enough.
Out of the Woods is statistically a hit.
Wildest Dreams went top 10 on the Hot 100 a month after the music video premiered.
If "1989" was released with new material you know damn well it would be guaranteed Hot 100 top 10. 
Laughable tries.
