First and foremost, a clarification is necessary: there is no "outer thigh" muscle. The quadriceps and hamstrings overlap onto the outer portion of the leg. There are inner thigh muscles (hip ADductors). There are no outer thigh muscles. The outer thigh features a strip of connective tissue (fascia, specifically) called the iliotibial band, which basically connects the hip and hip muscles to the knee.
To improve the muscles that overlap onto the outside of the thigh, other basic exercises can be performed. For example, the leg press and leg extension target the quadriceps (on the right side of the diagram). The leg curl is an effective exercise for the hamstrings (left).
As far as the butt is concerned, the gluteus maximus' primary function is to bring the thigh straight back (in addition to another function that isn't relevant to this discussion). This is done on a leg press, squat, or butt blaster. The smaller muscles: the gluteus minimus (under the gluteus maximus), the gluteus medius, and the tensor fasciae latae do abduct the thigh (move it away from the body) when the hip is straight or nearly straight.
In essence, to work the glutes while performing hip abduction, you either have to stand, lie down on the ground, or recline the seat on the machine that you use (which isn't possible on most machines). If you perform the exercise while seated upright, you will only use a few small muscles (the most notable one is the piriformis) which are about the same size as your cell phone and therefore, are metabolically insignificant. These muscles are inbetween the hip and pelvis, and lie underneath the glutes. Improving them will not change the shape or apprearance of your butt. So, unless there is a specific functional purpose you are using the seated hip abduction for, recline the seat or drop the exercise altogether. There are better choices.