First, while there may be a questionable study done in a third-world country that showed masks to have minimal effectiveness in stemming viral transmission, since World War II there have been 10 out of 10 studies that showed masks to be completely ineffective in stemming viral transmission (University of Hong Kong research team). It was from these studies that the Great Fauchino, then-surgeon general Dr. Jerome Adams, the CDC and WHO all initially said masks do nothing to stem viral transmission and not to bother wearing them. Then, out of nowhere, the CDC under the bidding of the Great Fauchino came up with the idea of everyone wearing a mask. It wasn't too long ago the Great Fauchino admitted there was no science behind this, as documented here.
In addition to the study done in Bangladesh, there were two other RCTs done on the effectiveness of masks in specifically stemming Covid transmission, one in Denmark and one with our own Parris Island marines. Neither study showed masks to do anything to stem viral transmission.
As for the Massachusetts study, the study period coincided with not only a sharp rise in cases in the United States but also in Massachusetts. Since only two districts were involved that required masks, that's not a large enough sample size to have any validity. But as long as we're talking small sample sizes, last year my oldest kid's school required masks for a three-month period while my youngest kid's school didn't (same age range). The school that didn't require masks had no more cases than did the other school. Down the road, Chatham County (GA) schools requires maks for months while neighboring Effingham County didn't. Effingham County schools actually had fewer cases on a per-student and per-teacher/administrator basis. There are also other studies showing masking in schools did nothing, either.
And not only that, there are many, many studies such as the one linked in the thread starter that showed masks to be completely ineffective - studies that you ignore. But let's assume you're right, that masks work in stemming viral transmission. Under that philosophy, as a society we are required to wear masks in public at all times because it would save lives. Is that a society in which you want to live?