Because they pick trees that have gender. They plant male trees, see dogwoods, the flower but not bare fruit. So you get allergies because of tree cum. And as far as I know plankton cum doesn't come with side effects.

Because Trees are for rich people only.

Poor people don't get natural shade. They just get to see "luxury" apartment towers with tenant only "public parks from a distance.
/s

All safely contained in an airtight tank so that pesky O2 doesn't escape back into the atmosphere

They grow upside down

the shade is also important

easier to digest

I don't even understand which part of the tree experience these tanks are supposed to replace. Are they really just there to pick up CO2? Because you can also plant a forest outside the city for that.

You'll miss out on all the other tree benefits, but so you also will with these glass tanks.