Probably the same reason none of the ones here stock it...They suck.
The 3200's do seem to have a reputation for overclocking, but so do the 3500's and as JKDDragon pointed out, thats if you get a decent overclock, there are a great deal of instances where you can't get a very good overclock, a good example is my AXP 2800, yes its a different era and architecture, but its the same principal, lots of people got great overclocks on it, but the best I've ever been able to get mine to is the equivelent of a 3200, and it was unstable, even at speeds equivelant of a 3000 it was unstable, I think the heat and my RAM may have had a factor in that, but still, I know I'm not the only one who couldnt get a decent overclock on it. There are always dud CPU's in the overclocking department that perform perfectly at stock settings but just won't overclock well. Basicly what I'm saying is, while the chances of getting a good overclock are high, don't base your system around the possibility as it is only a possibility until you actually get it and try it out.