Why have only a small handful of states joined the u. n. since 2000?

According to the UN, they have 193 members. And acccording to the U.S. government, the only two states that have not joined are Vatican city (Holy See, which most likely would like to remain neutral on global political issues) and the Palestinian Authority, which is recognized by some members, but not sufficiently to deem it a proper state entity.

If you make it more clear i can answer it