iOS 13 still hasn’t showed up on my 6+ and i don’t know why?

iOS 13 is for the iPhone 6s / SE and newer.

iPhone 6 and 6 Plus will never get iOS 13, as those devices are too old and will never run iOS 13. They don't have enough RAM.

If you want iOS 13 - buy a newer iPhone.

iOS 13 is for 6S and later.

Because the 6+ is now too old and out of date to get iOS 13. Your phone only has 1GB of Ram and iOS 13 requires at least 2GB of Ram.