Because tf2 is designed in such away that any class that has an advantage from an unlock or just general weapons loses it in the name of game balancing from valve.
What's the fucking point of playing as a specific class if you have to switch to another one every 5 fucking seconds just to even make a difference in the battlefield.
hell you could just give the player a choce between the weapons of all the classes it'd be a better game to boot if they did, except the pyro which needs to be made all around more effective like it was supposed to be int he first place
http://forums.steampowered.com/forum....php?t=1252294
I mean I'd love to be a sniper if he had the sawn off shotgun of the scout as his sidearm and the bow if was made to shoot just as straight as the sniper rifle instead of having the arc of the pyros flaregun even when fully charged.