Even if you are giving your opponent something that they need, asking them to trade during your turn gives you an advantage in a few ways.
You should always trade on your own turn, rather than your opponent’s turns, so that you can use what you get right away. Even if you are giving your opponent something that they need, asking them to trade during your turn gives you an advantage in a few ways. First, a larger gap between receiving the resources and using them creates more uncertainty. It’s possible that they could have gotten those resources without trading if they had waited until their own turn. Second, asking them to wait and trade on your turn can put them slightly behind, and causes your opponents to build a turn after they otherwise would be able to, which gives you a slight advantage.