They use different voting methods, if I’m not mistaken.
Most cogent explanation I’ve seen is CCPGrey:
If we want to change the two-party system (which is a thing I would like to do), the first step is going to be correctly identifying the causes of the two-party system.
One of the big causes is that getting 15% of the vote means just as much as getting 49% of the vote - bupkiss.
