The just cause it looks cool
premisse isnīt that bad, and is a part of the game even today. Not all those lines, curves and other details placed on modern cars and edifications, for example, are really necessary. Design is a part of the game, is part of what make us to buy this or that.
So, I believe the same can be applyed to starfleet vessels. Of course that designs are a personal choice, so, what is beatifull for one, isnīt for the other.