I don't think it's that strange. I can't hit my max HR either, even following the guidelines you see everywhere. Warm up, gradually increase hr by 5 beats, hit the hill hard, repeat, that whole drill. I see higher heart rates after long efforts, or a 3 or 4 mile aerobic run.
That's not a medical problem or poor conditioning either. My theory, and it's just a theory based on the experiment of me, is that (at over 60 years old) it takes longer for my heart to respond to effort levels, so I redline my aerobic system before the heart catches up, then I'm out of gas before seeing the max HR.
If so the solution might be to ramp up more gradually. I don't have the patience for it since I don't use that number for much anyway, but it's worth a shot.