It's not that Apple insists on using its own data cable. At present, Lightning data cables that are allowed to be sold in the market need to pass Apple's MFI certification. Prior to this, Pinsheng sued Apple for MFI certification monopoly, and Apple could make a good profit through the data line. And Apple doesn't seem to want the iPhone to use Type-C in the short term.
It is understood that the US Patent Office has published a new patent of Apple, which will be Apple's next generation lightning waterproof seal design. Since the iPhone 7, Apple seems to pay great attention to the waterproof performance of devices. The new patent not only has waterproof design for mobile phone interface, but also has waterproof protection for data line. In fact, there have been rumors that the next-generation iPhone will adopt the Type-C interface, but now it seems really just a rumor.
In fact, even if Apple adopts the Type-C interface, it will not affect it to become the most profitable technology company in the world. Apart from data transmission, is Tpe-C really better than lightning? Not necessarily, since Apple has released a new patent for Lightning, Lightning may still exist as a dedicated data line for iPhone in the future. If lightning is lost, then Apple's MFI certification is useless.