My wife and I were walking through the Army Museum and we saw a complete transition from heavy armor and chain mail to almost nothing (heavy cloth) in the late 17th and early 18th centuries. We saw almost no transitional uniforms. We were wondering when exactly that occurred and why.
Advances in musketry towards the late 17th century made all but the thickest of metal plate completely obsolete, and in the late 17th century you also see dedicated pikes getting phased out for bayonets. With the position of musket man and pike man combined, cavalry had their utility significantly reduced. Cavalry had to be faster and more mobile after this period which effectively meant the end of superheavy cavalry.