Bus gates are very rare in America and actually I think AA probably has more than other Us carriers but regular use is still limited to a sub set of flights at a few airports. The vast majority of US airports do not use bus gates except in extreme circumstances. Culturally it’s not something we are used to and grew up to look down upon. Most American airports are really focused on a smaller main terminal and some form of long fingers either directly connected or connected by train where there is room for all planes to be connected by jetway.