Why is the nasal swab for coronavirus so deep?

It's because apparently the virus likes to hide way up in there.
https://www.mdanderson.org/cancerwise/is-covid-19-coronavirus-testing-accurate-and-9-more-things-to-know-about-covid-19-nasal-swab-testing.h00-159381945.html
https://www.oregonlive.com/coronavirus/2020/09/question-over-invasive-coronavirus-tests-debunked-nasal-swabs-get-to-where-the-virus-lives.html
https://www.usatoday.com/story/news/factcheck/2020/07/11/fact-check-covid-19-nasal-test-does-not-implant-in-nose-why-not-saliva/5405309002/

There are saliva tests, BTW.

Well, then why bother keeping social distancing...

Denisss,

Imagine that you are designing a test for coronavirus. You would want your test to be as accurate as possible. You would want to detect any amount of covid-19 virus in their system.

So how would you decide what patients should do?

Snozza I don't know much
I know I blow you so much
Let's not depend on a touch
Coz a conk is a river running so deep
Way down inside me it's up so deep
It's too big to hide and it can't be denied
My drip-tip's a river running so deep

The work's not hard to disgorge ya
I'd eschew hankies for ya
Nothing I wouldn't afford ya
Coz a conk is a river running soul deep
Way down inside me it's so soul deep
It's too big to hide and it can't be denied
My muke-puke's a river running so deep

All I ever, ever hoped to do
Was create a passage through
Which, just to breathe in, you should be leavin'
A little airspace so I can smell
You know darn well, I won't tell, no

I don't know much
I know I blow you so much
The lot depends like a crutch
And my leak-beak's a river running so deep
Away down inside me it's so so deep
It's too big to hide and it can't be denied
My droop-chute's a river running so deep