Chicken and egg. You can't have one store decide to not have a parking lot, because no one would go there. You could require all stores to be densely packed with no parking lots, but you can't force existing businesses to move or rip out their parking lots, so that would fail too.

Believe it or not, we actually have businesses that are so dense that walking between them not only makes sense, it's the only way to get around. They're called "shopping malls" and everyone hates them.

Shopping malls aren't disliked because they're dense - though the crowds don't help. Shopping malls are artificially constructed and specifically designed for discomfort, to force people to shop. Public seating is kept to a minimum, and benches are designed without backs, or otherwise to be uncomfortable, so people can't rest for free. Every available viewpoint is covered with shopping opportunities, in a consumerist assault on the senses. However much inspiration malls had from European town centres, commercial imperatives altered the construct fundamentally since.

> Chicken and egg.

Luckily, there are some developers with deep enough pockets that they can plan an entire district. It's been wonderful for revitalizing many blighted neighborhoods.