Considering that both are derived from plants, why is freezer recommended for coffee but not for tea?
"Both are derived from plants" is leading you astray. Tea is made from leaves, so does not freeze particularly well, like many other aromatic leaves (coriander, basil, other leafy herbs) that aren't recommended for freezing.
Coffee, on the other hand, is made from beans, which are much less subject to damage from freezing. There's really not any reason why there should be any similarity between the two.
Finally, neither are recommended to keep in the fridge (mostly because of humidity) and coffee isn't particularly recommended to keep in the freezer; it would be more accurate to say that it can be done with less detriment than tea.
From the Starbucks website:
Here are some more reasons why it is not recommended to keep it in the freezer.
It's not recommended, but it can be done to less detriment than tea would suffer. The reason it is worse with tea is covered in my first two paragraphs.
Typically, tea is made by fermenting and drying tea leaves , whereas coffee is made by roasting coffee beans, which are actually seeds
Both tea and whole bean coffee can be safely stored in the cabinet much like spices. However, once the coffee is ground, it starts to lose moisture, and therefore taste.
Alton Brown has a lot of great advice on this in "True Brew" http://www.foodnetwork.com/recipes/alton-brown/true-brew-recipe.html
The Food network advises: "Store whole roasted beans in an airtight container in a cool, dry place for up to two weeks. For longer storage, freeze whole beans, freezer-wrapped, up to three months. Since room-temperature ground coffee begins to go stale within a couple of days after it's ground, it should be refrigerated in an airtight container and can be stored up to two weeks."