Sure, people who are happy customers of quaternions and don't feel driven to understand what's under the hood, why change?
The pitch in the OP is (I think) intended for people who feel pressure to understand why it works. Geometric algebra can be built up yourself by picturing actual rotations, one dimension at a time. It's physical from the start. Quaternions are a finished math system that you have to reverse-engineer to understand. Some people like one approach or the other better.
Some geometric algebra people are kind of true believers. That's probably not helping the notation get traction.
Why not change? It's a good question. Learning about GA is an investment, getting it coded up and tested is an investment, and the obscurity of GA is going to make the code almost encrypted to people who aren't fairly mathy. Although quaternions are definitely crazier than GA, the sad fact is they're much more popular.
There's some return on all that investment. It might pay off or it might not. I think it's a design decision.
The pitch in the OP is (I think) intended for people who feel pressure to understand why it works. Geometric algebra can be built up yourself by picturing actual rotations, one dimension at a time. It's physical from the start. Quaternions are a finished math system that you have to reverse-engineer to understand. Some people like one approach or the other better.
Some geometric algebra people are kind of true believers. That's probably not helping the notation get traction.