Actually I find it quite logical that a trade civ wouldn't tax their population a lot.
If we look at our history, any city that was flourishing due to trade would have very low taxes and citizens would live very easy lives. This applies/d to cities all over the world from many different cultures too.

As for the entertainment possibilities, well I guess Brad designed them like that either to balance to race or because he thought of the race as one where they would constantly be business oriented thus not leaving much room for entertainment in their lives.

Lastly, as traders, they would concentrating their markets to outsiders, thus why they would have very little internal market development.

imho, the Korx make sense the way they are.

Some good points. Lower economy (due to morale hit) does make their trading skills more important. They also have some good starbase modulus (Refining line), so if they get morale or economy resources they'll use them betting then other races.

Still, kinda strange they don't start with Market Centers (even Drengin have Black Markets at start), considering their whole corporation background.

Trade routes: other races
Economy buildings: your own race

Anyway, from gamplay sense, it's not much of penalty since they do start with ability to build Economic Capital (and only capitols bring money in early game).

Still, from flavour standpoint it's kinda strange for race that sells anything to anyone to don't know how to utilize Market Centers from start.

try to steal, or trade techs with the Torians )
"Planetary Adaption" of Thala Empire is useful, too.