The main reasons people replace antennas is that they don’t like the look of them or that they’re in the way. Not everyone has a high clearance on their daily drive, if you have to constantly squeeze by something that your antenna keeps hitting, you may want to replace it with something better and smaller to prevent this.
There are also low garage clearances, which will leave your antenna bent. Or even car washes.
If you’re on that side of the fence, it’s an easy choice to replace it. The other camp simply doesn’t like the way stock antennas look. Which, relative to a Tundra, we can understand.