I believe it was mainly because of the East India companies monopoly on tea imports from China and India.

This is what Gemini has to say:

Tea's rise to become the UK's national drink is a fascinating story with several contributing factors:

Royal Endorsement: In the 17th century, Catherine of Braganza, wife of King Charles II, popularized tea drinking among the upper classes. This royal approval helped establish tea as a fashionable beverage.

East India Company's Monopoly: The East India Company held a monopoly on tea imports, making it a readily available commodity in Britain compared to other European countries.

Lower Taxes: Compared to other beverages like beer and gin, tea had lower taxes, making it an affordable option for the working class.

Social Rituals: Tea drinking became ingrained in British social culture, with the development of traditions like afternoon tea and tea breaks.

Health Benefits: Tea was initially believed to have medicinal properties, further boosting its appeal.

These factors, combined with clever marketing and the drink's refreshing and stimulating qualities, solidified tea's position as the UK's favorite beverage.