How would voters know who 'their' representative was with proportional?
Let's compare Germany with the US.
In the US there are usually two viable candidates. One Republican and one Democrat. Seeing how the third party in the US, the Libertarians have 0 senators (federal or state), 0 house members (federal or state), zero presidents, zero governors, we can safely say it's a solid two party system.
In Germany there are six viable political parties. SPD (traditional left) CDU/CSU (traditional right), FDP (Centre right), AfD (further right), die Linke (further left), die Gruene (Environmental left).
Germany sets a 5%+ requirement on political parties to get PR seats.
If it were at 3% there might be one or two other viable parties.
When a German votes PR they know that if that party gets more than 5% of the votes, their vote counts.
When an American votes, there's a large chance their vote doesn't really count. Especially if there's heavy gerrymandering or if they live in a place which has such a strong leaning to one of the two parties.
So, Americans can vote for whoever they like. But they'll get either Republican or Democrat and chances are their vote won't be that important in the large scale of thing. Germans can vote for who they like and 94.5% of those who voted, had the representation they asked for. Positive voting.
The representative is their political party. They vote for the policies they want, they vote for what that party stands for. They get that representation.
For example. A left wing environmentalist. They got for the Greens, chances are they'll get represented by the Greens.
A left wing environmentalist in the US will probably vote for the Democrats and get ignored by the Democrats because environmentalism isn't a key part of the Democrat's platform. In fact the Democrats and Republicans have to be kind of vague, except for certain key issues which generally go down to war, guns and abortion.
A clear example is the difference between the AfD in Germany and UKIP in the UK.
The UK has FPTP like the US.
In 2015 UKIP gained 12.6% of the vote and got one seat.
In 2017 the AfD gained 12.6% of the vote and got 90 seats.
Same percentage of people, for parties with similar aims. One leads to massive representation for their voters, the other leads to almost nothing because one seat in Parliament means almost nothing.