Of course not all masks are completely useless. By "these" I was referring to the item of the topic, namely "DIY masks". They are only somewhat effective in preventing droplets being transmitted when you cough or sneeze. They are less effective in stopping you coming into contact with the virus because they simply do not effectively filter it out.

What medical staff wear are masks that are effective at filtering out viruses. Read this [1] on the FDA site for a good explanation.

It's well established that there's a global shortage of masks. [2] They're made in China and they can only make so many because the manufacturing requires special equipment. [3]

[1] https://www.fda.gov/medical-devices/personal-protective-equi...

[2] https://theconversation.com/the-global-effort-to-tackle-the-...

[2] https://www.npr.org/sections/goatsandsoda/2020/03/16/8149292...