This is because the dominant respiratory pathogen is covid-19 not because you wear a mask.
It's very uncommon to have 2 floating around at the same time. Virology 1-0-1.
It's even less likely that influenza viruses and rhinovirus to co exist in the same season.
I'm not familiar with Virology 1-0-1. Do you have a link for folk with no experience to read this for ourselves?
I thought that the reduction in cold and flu might be related to social distancing and increased flu vaccinations? I'd be interested to read why this is not the case.
I have read an interesting article on Nature.com about this. It would appear when the schools went back in the UK colds cam back quite sharply. And TBH I think I've had a couple of mild colds towards the end of last year.
EDIT - here is the link for the article. Maybe those with Virology 1-0-1 might be better to comment on it and how accurate it is: https://www.nature.com/articles/d41586-020-03519-3