There are good reasons not to have proportional representation, at least not purely proportional. One downside to strictly proportional representation is that

There are good reasons not to have proportional representation, at least not purely proportional. One downside to strictly proportional representation is that a concentrated majority can make decisions without collaborating/cooperating with the minority. Example: Coastal states with large populations could just ignore the other states with small populations. The US bicameral congress balances the proportional House against the non-proportional Senate.