It wasn't always like that. Well into the 1990s (and even later, if you count the hangers-on who were already in office by then) it was possible for Democrats to win in conservative areas and Republicans to win in liberal areas. Parties just had to find the right candidate, by nominating someone near the ideological median of each state/district instead of the ideological median of their national parties. As a result, it was easier to get things done in Congress because there wasn't as much partisan or ideological polarization.
Yes. Democrats (or for that matter, Republicans) could unilaterally break this pattern by nominating people who can actually win in districts/states where they don't normally win. If Democrats want to win in the Deep South, they should find some anti-abortion Democrats. If they want to win out in the rural West, they should find some pro-gun and pro-fossil fuel Democrats. If they want to win in Appalachia, they should find someone who is practically a Republican but would also like to expand Medicaid and raise the minimum wage.
Republicans could do this too. If they want to win in big cities, they should find someone who agrees with Democrats on a lot of social and economic issues, but will also crack down on crime.
When one party starts doing this, one of two things will happen: 1) The other party will catch on and calibrate themselves accordingly to stay competitive, and we'll go back to much less ideologically polarized elections, 2) The other party will not catch on and we'll have a few election cycles where the party that represents the voters better will dominate the political system. Either outcome is better than what we currently have.