Probably the biggest factor is the conditions in their native habitat. The coconut in its native habitat(s) didn't have to deal with frost. So it didn't adapt to it. Butias, however, come from higher altitudes - regions where they experience more cold, so they had to adapt or they wouldn't survive. There are exceptions, so there's probably more to it than that.
Yes, the palm must evolve over time to cope with the cold or die. But, what makes it hardier? Yes, it is from somewhere where it experiences cold, but what biological factors make it able to cope with the cold?