The primary reason for not allowing everybody to drink from the cup was disease, mainly the plagues.
No it was practicality, as congregations grew larger and the Church became established in Northern Europe where grapes can’t grow.
People knew 1,000 years ago that disease can be spread orally very easily, and we still know that today.
Actually that would have been a very much minority opinion in 1007AD. People knew that you were more likely to get some diseases if you spent time near a person who had the disease, but the mechanism, if any, by which the disease was transferred from one person to another, was totally unknown. Even as recently as the mid-19th century, many respected doctors hotly disputed the idea that people could get a disease through their food or drink being contaminated with bodily or waste matter from someone who had the disease. And the plague is NOT spread orally.
To have hundreds of people drinking from the same cup is filthy and disgusting, and it is a very unhealthy practice.
There should never be “hundreds” receiving from one cup. If there are more than say 50 people who want to receive from the cup, you need more than one cup.
Leave it to the era that brought us “free love” to see nothing wrong with hundreds of people swapping spit from the same cup.
If the priest/minister uses the correct technique, the chances of “swapping spit” are negligible. Certainly no more than with the normal social/business interactions everyone does dozens of times a day (shaking hands etc.)
Anglican clergy have been offering the cup, and drinking the remainder in it, for 450 years. They do not have a higher rate of infectious disease than anyone else in the population, in fact actuarial tables used by insurance companies show that they are healthier and longer-lived than most other occupations. (I guess that will change now that some of them are practising homosexuals.)
Actually I heard that one diocese sought medico-legal advice as to whether it might have a financial risk from any communicant suing the diocese because he caught an infectious disease through sharing the chalice. The reply given was that the risk was negligible, and that the most likely (though still a very small probability) way to catch a disease through Communion is by receiving the Host on the tongue! Perhaps some of our posters in the litigious USA could confirm this.