There's a spectrum of density, and perhaps the sweet spot for front-porch interactions is somewhere in the middle of that spectrum. I live in a neighborhood with ample front porches and sidewalks -- and I've heard it referred to both as a suburb (by dense city dwellers) and "the city" (by people who live further out from the dense urban core). But it's easy to imagine both a dense city neighborhood and a semi-rural far-flung suburb with no front porches and no culture of interacting with neighbors.

Even the definition of "outside the urban core" is hard to pin down; I'm pretty sure you could get disagreement on whether where I live is within the urban core or not.

Suburbs have sidewalks but nowhere to walk to.

Yes, counterexamples exist. But the vast majority of American suburbia is quite like what you describe: isolated homes with very low density where the only way to get to anything you’d want to do is drive, even within the neighborhood!

I don’t have a front yard in my home in the city. But I do have a million things outside my front door. So I walk to them, and I see and meet neighbors along the way.

But you know what suburbs typically do have? Pleasant areas to walk in.

I walk my dog and meet neighbors who are sitting outside their houses. I also sit outside my house and meet neighbors who are out walking their dogs or just out for a stroll.

When I've spent time in big cities I simply don't see this, because there aren't good places to walk dogs and it's generally unpleasant to just be out in the street for the sake of it.

The idea that all suburbs are isolated nightmarish hellscapes of pavement and car accidents is some combination of a myth spread by city dwellers and a minority experience in a few types of McMansion housing developments.