Update the ios on the 6 Plus to 13

My iPhone 6 Plus updated to 12.5.1, seriously Apple can’t bump it to 13? With the current phone the latest Apple Watch I can get is a used series 2. I would like to get at least a series 3, and some of us can’t afford to just buy another phone for the privilege to buy an Apple Watch. There’s a lot of people out there that have the older 6/6plus.