You'd have to ask previous governments.
We sat on the Security Council once every 10 years, once every decade, from the get-go, and then we lost out. The Security Council, for all its faults...and right now it has a major fault, in that there are major vetos. The veto is being used. They have been unable to reform the voting structure. The five permanent members are unlikely to give up the veto, despite the fact that very good proposals have been put forward for a change in the structure to enlarge it and to change the voting structure, etc. As long as the veto holders hang on to that, it's unlikely to change. Given the relations with Russia right now, the Security Council is much more stymied than it has been since the end of the Cold War.
That said, the Security Council is still the place where the big decisions are made for international peace and security.