Alcoholic beverages as a whole have had a sanitary role for long: in the antiquity water generally was not drinkable and alcohol having antibacterial properties made beverages safe for drinking. The bible does not give water a beverage, and only a few Greek texts talk about it. In the east, on the other hand, water was boiled to make tea, which killed pathogens [hist 7].
As the European population increases, the number of bees decreases relatively. The demand for honey increases whereas the production stagnates, prices go up. Around the Mediterranean, grape culture is cheaper than beekeeping. So wine becomes early (proto-history?) more common than mead. Egypt and Babylonia seem to have preferred beer very early.
In the part of Europe where no wine can be produced, England, Scandinavia, Eastern Europe, England, the consumption of mead went on and an unexpected phenomenon is responsible for its ending: reformation. Luxury of catholic churches and their candles is over, protestant austerity is harmful to beekeepers who lose about half their income due to the drop in the demand for wax that churches used a lot so far. If the whole income of beekeepers is to come from honey, prices have to increase and mead is really not affordable any more. The only countries not producing wine which did not turn protestant are Poland (catholic, the pope is Polish for instance) or orthodox countries such as Russia. Gayre notices in hist1 they are (in 1950) the only countries where mead is still drunk [chapter 8 de hist1].
Gayre in hist1 almost has a heart attack every other page when he talks about tastes concerning mead. Recipes depend on supplies: if grape is cheap some is added to the mead, if malt is cheap it is used... But recipes also depend on the tastes of customers of that time.
In Viking mythology, the wife of the god Thor gives some aged mead to the god Loki. So Vikings considered aging as improving mead, as gods drank it aged. It must still have been drunk young (at the end of or during the fermentation), that is still sweet.
From the XVIth to the XIXth centuries dessert wines are fashionable at the English court. Wine was imported from Canary or from Crete. Porto, Sherry, Madeira were also imported in the XVIIIth and XIXth centuries. So it is likely that mead had to fit the mainstream tastes and was made sweet. Gayre says that queen Elizabeth even added some sugar to sweet wines.
From the Middle Ages, mead is so expensive compared to wine and beer that only rich nobles could buy some. But not only they could drink mead. Peasants drank some they made themselves. Beekeeping techniques made the extraction of honey difficult: at the end remained a mixture of honey and wax that could not be sold. It was mixed with water and fermented. Gayre states that peasantry, having scarcely educated a palate, preferred sweetness. It is true that children for instance prefer sweet food. But Gayre's views are obviously too condescending: the food of the rednecks in many countries is much better than the one of the court of his country. Additives (spices, herbs) were required to make this syrupy "mead" drinkable. It was doubtlessly drunk young. Not precisely the drink of the gods.
As mead was much more expensive than table wine, its sale was complicated. But as sweet wines were imported from Spain, Italy or even Crete, they were more expensive than (French) dry wines. So the marketing must have made mead makers focus on this niche were they could be competitive. Unlike wine, mead can easily be made dry or sweet at will.