For one, the bobbin size. The 29 does not have a big enough bobbin to do a pair of shoes. Second, the wheel provides constant pressure on the work and provides better control. Another, is you can change stitch per inch much easier on a post bed. I’m not sure you can change the number of stitches on all 29 models. Typically, different styles of shoes have a different stitch count. My Cowboy 810 can do 5 - 21 SPI, I believe.
I recommend checking out Marcell Mrsan’s channel. He mostly does shoes but the same principles apply in upper making.