I recall this being addressed in an Anthropology of Food class I took. IIRC the reading was "Time, Sugar, and Sweetness" by Sidney W. Mintz in Food and Culture: A Reader. Though the reading focused primarily on sugar, it does speak a little regarding tea and the arc of the two is largely side by side.
Originally, they were high class items owing to their rareness and the expense of importing. The high price they fetched spurred the creation of the global colonial and trade structures that could import them in regularity and quantity. By the time of the Industrial Revolution, the increase in supply rendered their price point within the reach of the common worker.
Meanwhile, big changes in society are changing the ways people eat. A common meal for a pre-industrial laborer would might be something like oatmeal and milk, with milk and oats likely produced by themselves. Once the laborer had migrated to the city for factory work (as many did), the common food was no longer the local produce common to the region. In its place were the some of the most common manufactured and imported foods and drinks, tea and factory-made bread (often with jam and sugar).
No doubt a large part of their prevalence was the ease with which the new meals fit into relentless shifts at the factory. The tea could brew while you worked and the bread was pre-made; you just went and got some. This removed the otherwise normally large amount of time a laborer would spend ensuring their own food supply, freeing it to be used for labor. The stimulating effects of the caffeine even assist in staying alert through unbearably late hours.
Presumably the rich drank it because they liked or saw advantage in drinking it. It had become a sign of refinement way back when it was rare and expensive. I would speculate this symbolic aspect endured the loss of rarity in the act of buying rarer teas and participation in acts of etiquette.
So it came to be that, through its colonial empire, everyone in Britain had access to tea and, through industrialization, an overwhelmingly large part of the urban population was drinking it several times through out the day. This happened for long enough that it became a cultural touchstone.
hi! not discouraging other responses, but you may be interested in these posts on early British tea consumption & trade