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.

The alternative right now is the minority having total control over nearly all federal and state bodies of government in the nation. I'll take the 'risks' of proportional representation over that...