Crossbow bolts are shaped, and when penetrating armor, the important factor is force per square inch. A hardened steel tip has a higher chance to penetrate armor than a soft deformable projectile, as the projectile flattens, decreasing the pressure, and then caroms off.
Crossbows do NOT make a greater role despite being more effective at piercing armor until high power rifles were invented, the thing was the change in tactical setup.
For some perspective(grossly simplified, and varies by region of course)
Early eras had infantry dominated warfare. You used loose formations of of individually strong warriors fighting against similarly loose formations. There was a low focus on occupying ground. Real armor and longer blades were not available yet, but it worked well with difficult terrain(and still does, its still used for urban warfare).
Then formation warfare turned up. Phalanxes and formation fighting lets them take on loose and ill disciplined formations at low losses. They were very good at claiming ground and holding it, plus greater use was made of inexperienced warriors. You generally had rookies acting as light infantry to take the brunt of first contact, and better equipped veterans acting as piledrivers to punch through. This was slow(tactically speaking, strategically they moved incredibly fast with marches), however, and eventually gave way to...
Cavalry, specifically heavy cavalry, with good equipment(this meant only nobility need apply). This went somewhat back to the elite unit model, where a number of seriously expensive units were backed by massed infantry to hold ground. You used heavy cavalry to go all over the battlefield breaking up formations and heavy infantry(two handed swords etc) to deal with pikes.
Then came archery in warfare(it existed for a while already, but there was a low focus level on missile warfare, since it was difficult to train), particularly with massed archery volleys. These were great against pretty much everything but lighter cavalry(which could close the distance. Pile arrow volleys could break heavy infantry or heavy cavalry formations if they hit, and being light infantry, archer units were more mobile than most infantry. This led to the rock-paper-scissors of combat, light cavalry against archers, heavy infantry to counter cavalry and screen archers from close range retaliation, and archers to deal with heavy infantry.
Then came the crossbow, which changed ranged warfare by making it much easier to get into. While possessed of a lower rate of fire than bows, they had comparable penetration and you could have cheap light infantry that could trash costly heavy infantry. At this point, armor proper became more of a matter for leaders and other noble units, warfare was mainly peasants vs peasants.
With heavy infantry on its way out, you then see the development of anti-light armored warfare. This made it practical for things like the rapier(made for street fighting) and the gun, because for common infantry, armor was getting lighter and lighter, and they worked just as well as a crossbow against those. The reverse was true for heavy infantry and commanders, plate armor was designed to counter guns specifically, and got thicker and thicker as muzzle velocity went up.
It goes further of course, but most people are more familiar with modern warfare.
