Because in most people the left brain and right brain are poorly integrated.
Because neither side integrates the other side’s facts, observations, & concerns into a coherent whole. Mostly, each side tunes out everything the other side says.
Thomas Jefferson was right – we don’t have to have political parties. We have them because most people’s brains are badly fractured and we don’t or can’t integrate all of the facts, observations, & concerns into a coherent whole – a shortcoming most scientists have as well.