Those add substantial crossing time and are quite costly.

None of the world's great walking cities heavily uses bridge crossings like that.

If you are in hurry, you will avoid those. They add more time to your trip then one would guess intuitively.

What do work for pedestrians is a network of smaller roads that you can "just" cross safely without waiting or taking detours. Basically, a few big roads you cross once in a while and the rest being smaller roads where cars are forced to go slowly.

" without slowing anyone down. " - but the very first image you provided will slow down pedestrians, it's harder to cross compared to a simple direct crosswalk and it's less friendly to ppl with mobility problems. Such bridges are relatively ok to implement outside cities where you have highways/roads with cars driving high speeds but these are bad solutions inside cities where the priority belongs to pedestrians and cars must drive slower

It's inconvenient to climb a set of stairs every time cross a road. What about pushchairs, wheelchairs, the elderly, people with walking sticks, shopping trolleys, arthritis, gammy knees, people carrying heavy shopping or wheeled luggage? In general if you're going to slow down anyone then slow down drivers who have engines to accelerate them back up to speed with no effort. Making people climb stairs so drivers don't have to wait is not good pedestrian infrastructure, the view (of a road full of cars who have priority over you) is hardly a great trade off. Nor is paying the extra taxes for bridge maintenance so that car drivers can have a better life at your expense.

When you consider that drivers are generally wealthier (because they own cars) and the pedestrians are breathing car exhaust and tyre dust while working their lungs harder climbing to give cars the priority, listening to car noise while drivers pass in low effort comfort, the mild unfairness of it is more starkly contrasted.

Ideally good pedestrian design would tempt people out of their cars because walking is so quick, convenient, cheap, pleasant, interesting - with shade and shops and short distances and quiet clean surroundings. Big steel bridges don't contribute to that very much. [Have you seen how often Americans comment on the price of gas? Yet what people campaign for is the government to lower the price of gas, not for the government to make life without cars so pleasant that cars are not a necessity. What sense does that make? Most living Americans have never lived in a walkable place, and have no film, tv, or cultural reference for one to use for a basis for such a campaigh - maybe Disneyland (which visitors tend to love)? 120 years ago everywhere was walkable because there wasn't much other than walking. 70 years ago places were bulldozed for cars. Now multiple generations have grown up and lived their adult lives with car dependent urban design].