Why are skirmishers so slow?

One thing that's always bothered me, skirms are really slow for the role they play. In other games and IRL, skirmishers are faster than normal infantry, meant for hit and run attacks using thrown javelins.

In AoE2, they have the same range and speed as arbalesters. I'd expect higher speed and lower range. For something you theoretically send first into battle to bait melee units and tank or dodge archer fire, they're pretty slow. This is also frustrating when you're trying to counter longbowmen with skirms and they die before they can even get close. On the other hand, they're oddly good at acting like archers and standing still while they snipe enemies.