Ds, like it or not, have a reputation of being a party of coastal elitists who all went to elite schools and became lawyers. Walz is the exact opposite of that. Midwestern state school education. Public school teacher. Football coach. National Guard member. Heck he coached a team to a state football championship. It does not get much more apple pie normal american than that.
So, while he has championed progressive policies in MN, he comes across as more your typical neighbor next door rather than your wealthy relative, who seems out of place, visiting from the one of the coasts.
In the end elections are more about personalities than policies and Walz's personality reads "normal guy" no matter how progressive his policies are.