While it certainly is a noble endeavor, there are reasons why people tend to build up some reserves.
1. If you get down to zero before you order more tea, you are forcing yourself to go several days if not weeks without any tea.
2. Variety, if you are the type of person that only drinks one type of tea, this is likely not an issue. But for us for lack of a word omni-teaists it is hard ( read near impossible) for find a single vendor that does many different types of tea better than average, and I am pretty sure there is not a single vendor that does all types of tea even average. So why not stagger orders slightly and replace gaoshan when they are running low, and Japanese teas when they are getting low, etc...
3. Sometimes you just buy a bad tea. I think (besides puerh people) this is the number one reason for building up excess tea stock. Even just 50 grams of bad tea can feel like a chore to drink, actually causing you to prolong the time until you order more tea if you wait to go to zero, because you will starting asking things like "Do I want to have some horrible tea,or do _______ instead?" The more you need to ask that question the more likely you will skip drinking tea.
In fact I did not place a tea order this month, and I likely will not next month either because my tea drinking is way down, but I have a lot of good teas that I want to drink, to reduce my stock, before I even think of ordering more.