I think it's interpreted as the licensor can add whatever clause they want and it has to be followed, and those terms say that a licensee cannot add additional

I think it's interpreted as the licensor can add whatever clause they want and it has to be followed, and those terms say that a licensee cannot add additional clauses to that of the licensor when it redistributes the licensor's work or derivative work. Basically, I wrote the code, I decide. I give it to you under my terms. You cannot go give the code to someone else under new terms, because I prohibited you from doing so when I gave you the code.