Probably because you haven't watered them enough. For the first year of their planting the roots will need to be kept permanently moist while they re-establish themselves in their new location..
On the other hand, if they're Lleylandi conifers and planted immediately up against your neighbour's fence, he's probably terrified to death that in 12 months time they'll be as high as his house, cutting out all his sunshine and sucking up all water from his garden, and he has poisoned the roots. (And who could blame him with the trouble these wretched anti-social plants cause !)