Torchwood and Hover Goat question

My guess is to minimize the work it took to add them. If they could be customized they would require new abilities, a boat load of cosmetics and the work needed to add all of that. For a class they outright said would not be getting variants that is a great deal of work. (Especially since maintaining GW1 and fixing game breaking bugs in GW2 is apparently too much effort.) In short, far too much work for little to no pay off. (Which as a player sucks but as a company is just common business.)