There are a few ways it could happen 1. it's imposed on them by an outside force like through a voter referendum or court order 2. the party is currently in po

There are a few ways it could happen 1. it's imposed on them by an outside force like through a voter referendum or court order 2. the party is currently in power but thinks it might lose power soon, they could adopt this on the way out to limit the ability of the opposition to get a supermajority but in a way that will be harder for opponents to object to compared to other things they could try.