If masks help, why do RCTs not (on balance) show they help? Surely if they helped, then the evidence would consistently show this, rather than null/negative effect?
For every legit study showing they don't help there are more legit studies showing they do help. Whenever someone posts one of those studies showing they do help here, people nitpick it in a way they don't nitpick the studies showing it doesn't help. So the answer to your question is confirmation bias.
Nonsense, I nitpick them all. I've regularly stated in this thread that almost all the mask studies are very poor. Non-randomized, very small sample size, and otherwise very low on the tiers of evidence based medicine. And even with that, there's no strong signal in any of them. Most of the studies show no significant effect, while others just barely edge into significance. More importantly, most of the studies don't even measure what they need to measure if they're to have any relevance to public policy. 100% of the studies before covid, and most since, looked at N95 (mostly) or surgical masks (occasionally) in clinical environments. There were exactly zero studies that looked at cloth masks, and exactly zero studies that looked at mask use among the wider population.
The two studies that fall higher on the tiers of evidence based medicine are the Danmask and Bangladesh studies. The Danmask study shows no effect, and it seems to have held up pretty well. I haven't seen any substantive criticism. The Bangladesh study showed an effect, but had numerous methodological problems that we noted in the thread, and since that discussion medical statisticians have been given access to the raw data and came up with some more problems. Which is really disappointing, because it's the largest study by a big margin.
So at best, masks could have a small effect. Or no effect at all. There's no evidence whatsoever they have a strong effect.
I thought masks were a reasonable precaution at the start of the pandemic, because there was a lot of misinformation about the deadliness of the disease, and we really had very little idea how the virus was spreading. But as evidence came out supporting the highly aerosolized nature of the disease, the case for masks was demolished. The studies since have supported that conclusion.
Masks have known negative effects. They can spread disease, some people have difficulty breathing, and most importantly they hurt socialization for children. Since those are real and damaging downsides, and the potential upside is at best dubious, there's absolutely no justification for this obsession with masks, and the lack of attention to things like ventilation that have a much greater effect.