Typical British teabag tea -- the stuff we consume in quantity -- is brewed with water just off the boil, and consumed often pretty quickly afterwards because cold milk gets added.

(Or it goes into a teapot for brewing, and again needs to be just off the boil for that)

Given that we can boil a kettle for a mug's worth of tea in not much more than half a minute, there's no reason to use them, I think.

And to follow up on this thread because a similarity occurred to me in another reply, we do use samovar-type things (electric tea urns) in other contexts (ad hoc and mobile catering), but that is about brewing the tea itself within the vessel and it requires both a different kind of tea and a noticeably different kind of scale (simultaneous volume). You do sometimes see those in company canteens though.