In reality, the usual suspects were pushing conspiracy theories about the CDC even before they determined masks were useful. A famous conspiracy peddler famously claimed the CDC was downplaying how bad the virus was and 'it was over for humanity, it'll only be lone survivors' when we only had a handful of cases in the US.
In other words: the CDC could've nailed every single guideline and we'd still have half of the population making up conspiracy theories about it. It's just too politically convenient.