Do you think they have/had Alexander and Chi Chi on the team because they like them better as people? Before questioning the GM, take a moment and try to find the reason why they have gone with Rodriguez, Alexander and others before Small.
Nobody can read the GM's mind, but perhaps it is Small's BB/9 ratio of 5.0 in AAA which suggests he may have major problems with walks in the big leagues. After all Small did walk 4 in the 2.2 big league innings he pitched earlier this year. In fact, Small is walking more batters per 9 in the minor leagues than Burnes, Woodruff, Lauer, Houser, Peralta, Ashby, Alexander, Suter did in the minor league careers. That's most likely why he is still in the minor leagues, they're not going to call up a pitcher to a contending team simply because he was a former first round pick and is in AAA.