That’s only true around landing and takeoff. For the most part their navigation relies on hybridized data from their inertial, air data and GPS, with several redundancies in place for bad readings and cumulative errors. Among all of this autonomous measurement apparatus, the GPS is the only part that doesn’t require numeric integration from speed or acceleration data to yield a position reading, and thus it is the only one that doesn’t drift over time. It’s actually fairly important, and it’s why using the gnss jammers you can find on amazon is super illegal