I have no doubt that this will be move, but here we go.

Knights were very well trained, and well armed. The heavy armor they wore was a major factor in there victories as well as there defeats. Weapons an tactics were always being developed to deal with armor. Polarms, war hammers, crossbows, all came out of the need to deal with armor.
Then you had the fact that there were different orders of knights. Each with slightly different rules and organization. They all were basically ruled by a church that was more interested in a few goals rather then fighting in any type of strategic way. I mean at one point the pope out lawed crossbows.
So there armor held them back, to a point. There rules held them back, and there church held them back. They never had a chance.