It is normal. Everyone is diffrent thats just where your freckles ended up my gym teacher has the same freckles at the same spot. Its normal dont worry about it
Why is it that I have freckles on my shoulders, chest, arms, face, etc., but only very few on my legs?
Freckles are little areas of the skin that have more pigment than the ones of the surrounding area. That is because there's more concentrated melanin there.
Their number is actually genetic and they usually appear on the face and arms. The fact that you have more freckles on your arms, face, shoulders and few on your legs it is due to sun exposure.That's because, although freckles' numbers is genetic, their number and visibility can increase when exposes to ultraviolet rays (UV).
Sunlight (and suntanning as well) emits UV which cause the skin's pigment to produce more melatonin at an increased rate. Seeing that there's more melatonin concentrated in those areas, when the melanin production increases, your freckles will become darker and more visible.
Now, especially in the summer, your face, shoulders and arms are the areas that are most exposed to the sun compared to your legs so that's probably why you can't see a lot of them there. You should probably use sunscreen for those mostly exposed areas even when you go out daily.
Hope this helps!