Assuming you mean COVID-19 it's because the virus is not airborne, confusing since it can infect you "through the air".

The virus lives in droplets of bodily fluid, when you're closer than 2m just speaking with someone else is enough to exchange droplets and spread infection.

It's of course possible that someone walking by your window will cough out some droplets and they might be carried through in the air and infect you but the aim of the social distancing precautions is to reduce the infection rate and spread, not to prevent anyone from ever getting the virus.

Gravity tends to with against having viruses lingering in the air.

And there is as minimal viral load you need to be exposed to, to actually get you infected.

So there is a low chance to get in contact with the virus, a even lower getting in contact with enough viral load to cause you harm.

The distance (and potentially masks) serve the purpose to get the density down to point, where it doesn't matter.

The evidence we have so far shows that the vast majority of cases are transmitted indoors:

https://www.medrxiv.org/content/10.1101/2020.04.04.20053058v...

In practice, a transmission event happens through a certain amount of virus particles entering the body, and this doesn't seem to happen very often for Covid.

It seems that infectious people mostly don't expel it in small enough drops for it to linger.

Of course it isn't settled, but this is what all the discussion about droplet (doesn't linger) and aerosol (lingers) transmission is about.

According to the DHS (I’m struggling to find a source that isn’t the White House slides, which I loath to link too) COVID-19 has a half life of about 2 minutes in sunlight on a warm day (21C).

So we’re safe from lingering viruses because COVID-19 doesn’t linger that long outside.

As viruses go COVID-19 is pretty easy to break down, and doesn’t last that long in the wild (especially compared to things like bacteria). But it’s still virulent enough to cause a pandemic, despite being pretty easy to destroy using light and alcohol.

Statistics and probability.

Sitting next to an infected person at work, cinema or bus for a long time will expose to a large probability of being infected several times with a high viral load.

Walking past an infected person the probability is low, the viral load hopefully quite dispersed.

Though getting too close to heavy breathing and sweating jogger is not recommended.

I wondered this to, and heard it explained by our radio doctor (Dr Karl in Australia). Coronavirus needs a lot of virus to get an infection - around 100,000 virus particles, whereas some others can cause an infection with just 20, so walking past isn't enough, transmission requires prolonged contact with someone infected. (not a doctor)

See "it's less infectious than airborne viruses, like measles" at https://bestlifeonline.com/coronavirus-facts/

It seems like the primary transmission mode is through droplets, not air

Yes. But it lessens your chances of contracting the virus I suspect. And should you contract it via those means the viral load is likely to be reduced.

There are I believe 0 confirmed cases of virus transmission taking place outdoors, of the almost 4 million cases.

Edit - does anyone have data to contrary?

That's such an unlikely claim that the onus to show proof lies on you.

Well I heard this on Brett Weinstein's podcast where he reviewed literature showing this to be the case, a couple weeks ago at least. No doubt related to UV which has shown to kill the virus.

I'm sure you're aware that positive news about the virus is generally being censoring by mainstream outlets, if you're wondering why you didn't hear about it.