Look at it from his POV, he comes Arsenal and he plays europa league, without a guaranteed starting spot, and a manager in Arteta who doesn’t trust him, has treated him awfully and have his number away to a new 50m signing at CB. Or he could stay in Marseille a French club in the CL, where he’s a guaranteed starter, possible captain and a better chance of getting into France’s World Cup squad.
Add to that he must have had a word with Arteta who probably has said he’s coming as a 3rd choice CB.
It’s a no brained from his POV. Just a shame Arsenal lose out because of Arteta.