In any case, the reason why no Bounty Hunter seems to use the Reaver is the fact that the Buckshot is just better, overall.
Faster re-fire rate weapons aren't as loved as you would imagine. You need to be a consistent aim in order to do any real damage (something I've been working on because of the Vengeances on my [LN]).
Buckshots, however, land a few shots randomly, and you do as much damage as Reavers would if aimed carefully.
Essentially, you need good aim for that, and, seeing how many missile users are around, good aim is lacking.:P
the problem is that of many quick firing guns. - in theory, they are equally efficient or even a bit more than the slower guns. - in reality however - it is easier to inflict an equal amount of damage with a 2.0 high damage gun instead of a 8.33 low damage gun.
so lets say - your 2.0 gun does 1000 damage - meaning you need to hit the enemy once to do 1k dam. - your 8.33 gun does 200 damage. - you need to hit your target at least 5 times to do the same amount of damage.
that means - you need to keep your target focussed longer than with the instant damage gun. - which in turn means you can start to activly dodge earlier.
reavers also "feel" like they use more energy for the damage they really do, which is of course a side effect of that you need to hit more often to do the same damage, - calculating the missed shots - you end up with a gun that does less damage for more energy.
all that comes down to the fact that - when you apply a linear give and take to a gun - a 1.0 gun doing 2k damage is much better than a 20.00 gun doing 100 damage ( in most cases )
Some people do, but there are a few things. For one, Buckshots are slightly faster. While it probably doesn't make much of a difference, I'm sure there are people who go for them for exactly that reason. Another thing is they're particle versus laser guns, which at least previously, made a noticeable amount of difference (though I thought that may have changed - yes/no?). And as a last reason, they look prettier (at least in my opinion).
Reavers appear to do more damage, but also soak up a lot more energy.
Buckshots are also Particle, which do 1.2x damage to Graviton type shields, which are the most common. Where as Reavers are Laser and do 0.8x against Graviton.