I think its often said by those who have not lost anyone and they cannot comprehend how it feels, and often saying what they have probably read somewhere, thinking grief is an orderly, tidy, linear, brief process. When it is anything but! They probably are also saying it due to their discomfort - people often arent good with feeling uncomfortable when someone else is in pain (which of course doesnt excuse them, but in their way they are trying to say something they think might be comforting)
Try not to take their comments to heart, no-one can take away your love and your loved one. Take your journey at your own pace, knowing you have support here xx