I went through an entire education system that was built around the idea that every kid has a different type of intelligence. Musical, spatial, interpersonal, bodily kinesthetic and so on. Teachers loved it and it shaped how I was taught for years. Then I started reading actual psychometrics research and found that basically nobody in the field takes it seriously. How did a theory with so little empirical support become so dominant in classrooms?
This is one of the starkest gaps between education practice and psychometric science and it is genuinely frustrating 
Gardner never derived his intelligences from factor analytic research. He proposed them theoretically based on criteria like having a distinct neural substrate and a unique developmental trajectory. When researchers actually tested whether his proposed intelligences behave independently in real data, they found the same positive manifold that always emerges. Abilities correlate with each other rather than clustering into neat independent categories. The theory spread through education not because the evidence supported it but because it was ideologically appealing. Telling every child they are intelligent in their own way is a feel good message that resonates with educators regardless of what the data says 
Gardner’s theory became dominant in classrooms for the same reason horoscopes are popular 
It tells people what they want to hear and is vague enough that nobody feels left out. Great for morale, terrible as science 
Another popular influence, Mismeasure of Man, claimed there was no biological basis for intelligence. I’ve heard it is popular in college classes. When Intelligence pioneer Richard Haier pointed out research shows a correlation between brain size on CT scans and intelligence… the Mismeasure author ignored it.
“It is difficult to get a man to understand something, when his salary depends on his not understanding it.”
– Upton Sinclair