In the early Church each member of the congregation or family brought a loaf with them to Mass. The bread, usually a substantial size loaf was then usually placed in a communal group near or on the altar. After the consecration Communion would take place with the Priest either handing one of the consecrated Hosts, not necessarily the same one that was brought in, to the communicant, usually the father or placed a small morsel in his mouth and handed him the rest. That person then brought the remainder to the family, where a small portion might be consumed, not always, and the rest wrapped in a piece of cloth, usually white in color, and brought home for consumption during the week.
As time went on a decision was made that the Church would supply the bread opposed to the families bringing them in. Maybe some families brought in none at all or very small ones. Maybe they were monkeying around with the required ingredients. Who can really say? There is some evidence that in at least some Churches there were definite class divisions amongst the congregations, which also could have had something to do with it. Perhaps the wealthy felt they were getting shafted by having to supply more than did the poor.
In any event the Church, possibly with an eye towards economy started making the loaves smaller and smaller, In time the Hosts became basically what they are today, small individual size portions although the practice still remained of allowing the consecrated Hosts to be brought home
Due to a distinct lack of reverence, due mainly I think to ignorance and numerous acts horrific sacriliges that were occuring, Hosts being used as good luck charms, as amulets to ward of sickness, in magic spells to bring back lovers or ensure a good crop, to curse others, private expositions at home for which admission could be charged, used in Black masses etc., the Church forbade the bringing of the Hosts home except in the case of the Last Rites and went to Communion being distributed solely on the tongue.
A simple answer but you get the picture. It is fascinating to know that.today we still hear of those who try to do the same things. We’ve had posters on this forum ask for the best way to have a private exposition at home,and if carrying a consecrated Host near to the body is allowed, And we’ve all heard of the attempted sale of consecrated Hosts on the internet.