Your mask isn’t there for your own good. Wearing a mask may reduce the viral load you may receive if you’re exposed, improving the odds your immune system can stamp out any nascent infection, but that’s just a bonus.
The purpose of a mask in a mask mandate is to protect others from you in the event you’re infected but in the window between becoming infectious and becoming symptomatic and therefore aware (and possibly beyond if you’re the kind of person that knowingly mixes with others and coughs openly when sick). Because it’s for people who don’t know they’re sick, it only works if everyone does it. So it’s mandated for the good of the whole.
This was particularly important with the original strain of SARS-COV-2 because it had a particularly long incubation period.
The more aggressive variants since, along with more sensitive immune responses in most people due to vaccination, exposure, or both have shrunk that window significantly, but it hasn’t disappeared.
General, society wide, mandates aren’t imo necessary under the prevailing conditions, but that doesn’t mean there won’t be situations (close knit group with a spike in cases for example) where reintroducing such rules make sense.