I think it's because it doesn't really add anything special as an ability. The point of the SRMx/x, LRMx/x/x, IFx, & other types of abilities is that you're using something extra: the SRM/LRM abilities let you use specialty ammo to have additional effects, IF lets you fire even if you don't have direct LOS, etc.
Pulse weapons, however, don't have special damage, they just are slightly more accurate. Since the weapons with minimum ranges have their AS damages reduced to account for their reduced accuracy within their minimum range, it makes more sense for pulse weapons to have their AS damages increased to account for their increased accuracy.
If you wanted to do a house rule for that, you could...but then you'd also have to drop the base damage that they do as well. You'd probably see your base damages drop by 1 (or even 2) for each damage bracket, & then you're not talking about a whole lot of damage necessarily hitting the target unless your 'Mech is loaded with pulse lasers.
By the same token...if you're going to do that, then you'd probably have to have the negative ability of "Heavy Laser". You would get a slight adjustment to the base damages (probably 1-2 extra points at most), but if you don't exceed your strike role by at least 1, then you subtract the damage the listed amount from your damage.
AS is all about simplification. Trying to unsimplify it isn't going to work as well.