“Would the epidemiologist please explain the danger if everyone attending employs safeguards of masks, gloves and distancing?”
What follows is educated opinion, not backed up by rigorous research. There is still a lot we don’t know.
First of all, gloves are a particularly bad idea. Better to use hand sanitizer. I carry it around everywhere. I use it whenever I touch something. If you don’t use your local eruv and your rav does not approve of carrying it outside of an eruv you might want to stay home on Shabbat.
Masks don’t offer as much protection as people think. They do help to protect people from you if you are infected. The N95 mask is best but they may not be easy to obtain, and they aren’t always easy to fit.
The six feet distance may be too short, particularly if people are speaking or singing loudly, or coughing.
The shuls themselves may have ventilation systems that could spread the disease; it is possible to clean and disinfect them but it is quite expensive.
In my neighborhood, every shul is packed to the gills every Shabbat. We would have to massively increase the number of minyans if we were to allow people to maintain social distance. And the ventilation systems recycle the air, as mentioned above.
What follows is fact, not opinion:
We still have a lot of coronavirus disease, although our social distancing really did bend the curve. Montefiore Medical Center still had 191 hospitalized COVID-19 patients as of yesterday, but that was down from a peak of 1,148. New admissions dropped from 205 down to 15. But that is still fifteen people getting sick enough to be admitted to a hospital. And some suburban hospitals are NOT seeing a decline in admissions over the past few weeks.
Two resources I would recommend are the nightly videos by Dr. Stuart Ditchek, available on his Facebook page, and the statement by the Orthodox Union and Rabbinical Council of America updated today, available on the Facebook page of the Rabbinical Council of America.