It prevents YOU from getting OTHER PEOPLE sick.
If EVERYONE (and you're lying if you say everyone is masked in stores, it's simply not true) wore a mask, it would reduce the rate of transmission by a significant factor.
when you breathe out with no mask, your air goes everywhere.
When you breathe in with OR without a mask, you breathe the air around you.
When you breathe out with a mask, the air is kept CLOSE to you as it can't travel as far.
That's why they recommend distancing and recirculating the air - and keeping doors and windows open. It keeps fresh, cleaner air coming in to your mask so you're less likely to breathe in virus particles from someone else.
It's pretty simple. So you're not sick. Great! Are you sure? Remember, COVID's got a 5-14 day incubation period that may be entirely asymptomatic.
Are you sure 100% of the people you come into contact with daily aren't sick?
If EVERYONE wore a mask when out and about, and maintained distancing, we'd nearly eliminate the transfer of this disease. Science has PROVEN this.
All it takes, though, is one sick self-absorbed unmasked twunt in close contact to disperse the sickness across a large group. That's literally how this entire quarantine, distancing, and virology thing works.
Your point about basketball players breathing more may be valid or not valid - but it's immaterial. Just take COURT size. A standard high school basketball court is 84 by 50 feet. That's 4200 square feet for 12 people at a time. Each person has 350 square feet of space without even thinking three-dimensionally.
But wait - they aren't spread out that far, you say! Fine. Say they're all compressed in a quarter of that space. 87.5 sq feet per person. And that counts refs, EVERYONE. And again, the ceiling in my gym is 25 feet off the ground. If you add three-dimensional space it gets even bigger.
My band hall is 56 feet long by 40 feet wide. That's about half the size - 2240 square feet. If I have 50 people playing in my band hall, that's (about) *45* square feet of space per person.
But wait again! We don't fill the entire band hall! We sit in about half of it. Cut the space in half - now everyone only gets 22.5 square feet. And we have a 16 foot ceiling to boot.
Consider, also, that the walls in said basketball court aren't located directly next to the court they way they are in the band hall. A basketball court is MUCH bigger, with MUCH more open space and with MUCH BETTER AIR CIRCULATION. Risk of virus transmission is MUCH lower in a basketball environment than in a band hall, period.
I know we all want band to be "back to normal" but the fact is, simply, IT'S NOT SAFE.