They wear masks in China too but it didn't seem to make that much difference. Perhaps there would have been far more deaths.
The following is from a study published in June.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7323223/
"Thus, a pre‐symptomatic or mildly infected person wearing a facemask for hours without changing it and without washing hands every time they touched the mask could paradoxically increase the risk of infecting others. Because the USA is in a desperate situation, their Centers for Disease Control has recommended the public wear homemade cloth masks. This was essentially done in an effort to try and reduce community transmission, especially from people who may not perceive themselves to be symptomatic, rather than to protect the wearer, although the evidence for this is scant. In contrast, the World Health Organization currently recommends against the public routinely wearing facemasks"
Masks may make some difference (according to the study there's limited evidence), but it isn't just about wearing masks. Countries with less deaths typically stopped travel early enough to make a difference. Taiwan was one of the first to shut down international travel. They do have a mandatory mask policy on public transport but the quarantine rules on international travel and the rapid test and trace are more likely reasons for the low spread.
I should add that I wear a mask in public buildings and have no objection to doing so. But make it mandatory and you invite disobedience from the fiercely independent. 25 years trying to get people to do stuff tells me that voluntary observance is more effective. Especially if you can get enough compliance from the generally willing to make it the norm. And provided you have a supply of masks.