Levels on items

Why do you put same levels on items with different strenght? Isn’t that what levels are for, to show improvement?

Why not make the levels on items match the actual hero level? 

I’m a lvl 123 and, for quite a while, all items I saw were lvl 130, all item I have are lvl 130, and all items I see to buy are lvl 130.

What’s the reason for levels on items if all of them have the same level?