Everytime you drive your truck the heat put into the tires cause them to get harder. Sometimes the lack of grip at the end of life is a bigger deal than the tread depth.
I've replaced 2 different sets of tires that simply aged out- there was tons of tread left because the rubber had become so hard with age that they never wore. They consequently had zero grip as well. One set was so bad I could light them up in the dry from a 30 MPH roll in a FWD Ford Edge. It could barely get itself up a steep hill from a stop in the rain. Any kind of emergency moves or braking would have been impossible. Sometimes it's not about squeezing out the last 5K miles to save $100.
I've replaced 2 different sets of tires that simply aged out- there was tons of tread left because the rubber had become so hard with age that they never wore. They consequently had zero grip as well. One set was so bad I could light them up in the dry from a 30 MPH roll in a FWD Ford Edge. It could barely get itself up a steep hill from a stop in the rain. Any kind of emergency moves or braking would have been impossible. Sometimes it's not about squeezing out the last 5K miles to save $100.