This is a decarboxylation reaction. Decarboxylations are generally thought of as irreversible, because the product is CO2, which is a gas and thus the entropic cost of going in the reverse direction is so great that it is effectively irreversible. So in this case, the enzyme probably cannot catalyze carboxylation of GABA at a measurable rate under normal conditions. You wouldn't call it GABA carboxylase simply because it's an irreversible reaction and thus will not go in the reverse direction.
Enzymes known as carboxylases usually use CO2 in the form of bicarbonate, which is not a gas, and usually activate the carboxyl group (there are a variety of ways to do it).
But you're correct, the principle of microscopic reversibility applies to most enzymatic reactions, so they can catalyze the reaction in both directions. These enzymes can be named EITHER WAY (either way is valid), but typically, they are named for their most well known physiological direction. This might not be the direction where equilibrium lies.
For example, the enzyme most commonly known as malate dehydrogenase, which catalyzes the NAD dependent oxidation of malate to oxaloacetate, also catalyzes the NADH dependent reduction of oxaloacetate to malate. The equilibrium constant for this reaction lies very far towards malate (so if you write it as malate--->oxaloacetate, very far towards the left). So you would think, well, it should be called oxaloacetate reductase, since that's the direction of equilibrium, and that's not an invalid name for it, but it's commonly known as malate dehydrogenase because it is best known for being part of the citric acid cycle, and so its best known physiological direction is oxidation of malate, so it's called malate dehydrogenase.
