Because using crutch add-ons denies you the chance to become a good tank, and sets you up for total failure if those crutches ever break.
New content comes out, and optimal routes are not openly posted/figured out yet. While some totally reliant on addons tank flails about, I iterate my path over a few runs, and settle onto an optimal route.
First run where I prioritize making sure I have enough percentage, and figuring out how much each mob is worth.
Second run where I try shaving off.
By the third run, I’ve usually got a route that is 1-3% over, optimizing for smooth guaranteed routes, instead of ones that some random can screw up by butt pulling during some thread the needle skip.