I think the Vor are very, VERY invested in "there is no mutancy among us!" and could maybe afford to flaunt Ezar's new laws more regarding not killing babies. Whereas the lower classes--I think there was a shift, with the law; the law made it harder to get away with, so there was probably more of a judgment call made: is there something sufficiently wrong with this baby that it won't be able to work and will be a drain on family resources such that risk of arrest might be acceptable, or will it at least be useful in that sense?