Some countries think that western countries are simply looking for any excuse to prevent weapons going to them for their own political purposes. They're not quite convinced that we're sincere when we say that we just don't want weapons going to human rights violators. So there's a bit of suspicion.
There are harder-line countries that seem to believe there's some sort of western plot at regime change. They think that the real purpose of the ATT is to be able to give weapons to those we like and to not give weapons to those we don't like, and that there's a political motive beneath all that.
When we come out and say, “No, look, we just think that human rights violators should be prevented from getting weapons, that criminals and terrorists should not be getting weapons”, they don't think we're sincere.