Because non-certified iPhone lightning cables can spoil the iPhone Charging IC.
There are 2 types of iPhone Lightning Cables:
1. Certified iPhone lightning cable – recommended
You should buy only iPhone-certified lightning cables. It carries an icon sticker which says: Made for iPod / iPhone / iPad

Dual IOS-Android Lightning Cable
2. Non-Certified Dual IOS-Android lightning cable – not recommended
Firstly, this dual jack feels like it does not fit so properly. Only 1 side works and fits, the other side does not fit or work.
WARNING: Use this non-iPhone certified lightning cable will likely result in Charging IC damage and other potential problems.
#RobertReview (certified iPhone Cable): 9 |10
Published: 10th April 2019.
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Why Use Only Certified iPhone Lightning Cables?