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because they are using a layer 2 solution [1]

But even with lightning it's just cheaper but not free or is it?

For all practical use-cases it is. Last time I used LN (earlier today) it cost me 0.05% to send some money.

Considering that you'll need at least one Bitcoin transaction to use LN, then yes it's still expensive.

(You don't have to if you use more centralized solutions, which is what most use.)