Because so many people in the US drink tea in tea bags they are used to drinking tea one way. Boil water, bag in cup, add water, dunk tea bag, toss tea bag in trash, drink tea. Now that they are more interested in tea, they have upgraded the tea bag to a loose leaf sachet, but the process is still the same. Here is where we come to the learning curve.
All loose leaf tea (again I will say this is tea not tisanes & doesn't apply to CTC teas used in many tea bags) even those in sachets can be used numerous times to make a cup of tea.
Some are actually better for the second steep. Take Oolongs (or Wulongs) they can have multiple steeps and the later steeps are even more flavorful.
So the next time you are making a pot or a cup of tea, save the leaves or the sachet and resteep. Let me know what you think. Is it good, better, the same?