Knights were society’s most glorious gloryboys, and watching them clatter around on their gigantic horses wearing hundreds of pounds of shiny plate armor was an impressive spectacle that no one wanted to give up, no matter how many times they got aerated by commoners with longbows or drowned themselves falling into waist-deep rivers or whatever.
In the middle ages, European armies kept investing in heavy cavalry charges long after it had already proven ineffective as a battle strategy, presumably for one simple reason: it looked cool.
