It also depends on how you're hitting your muscles.
Example- I squat all the time, so even if I take a couple weeks off from squatting I will seldom get sore from it once I start again unless I do something different, like change the width of my stance, or wear a flat shoe as opposed to an O-lifting shoe, or go with a higher rep/lighter weight session.
Much of your athletic training, including weight training, has as much to do with your central nervous system as it does with your muscles. 'Muscle memory' is actually just embedded patterns of firing that your body stores in order to use less kinetic energy to move the weight. So if you start off getting back into training doing the same routines you did when you stopped, you might not be as sore because you probably haven't lost a lot of strength and 'muscle memory' as you think.
Solution? Try variations on your typical workout. If you barbell bench, for example, try going to dumbbells and alternate with inclines. If you do inclines, switch to a straight overhead press. If you don't currently squat or deadlift, start. You'll be sore. Oh yes, you will be sore.