You're the one who said killing you was probably the right call.
Exactly. But third things.
First, notice how he's pulled back from it originally saying killing him would be a smart play. He was trying to be gracious eagles. Should have waited to see who he wanted to take out first in order to prove his role. Mafia eagles would have fed us one mafia and then missed the next few days.
Second, mafia is in bad shape. They're down to 3 and they know almost all the civ specials are still around. They have stones, but don't have the numbers. They needed to buy time and make a play.
Third, thinking about it more, I doubt eagles is Thanos giving up two mafia. The way this plan would work is for Black Order A to fake claim and give up Black Order B who is in that group. That would mostly clear Black Order A and keep us hunting for another mafia in the same group. Meanwhile Thanos is in the other group collecting stones.