In the end of it all, that's usually the last half year at best of the expansion being out before the next one comes up. I've played other MMOs before that give you multiple types of weapons you can go after at once.
And don't forget the main point...NOT EVERYONE LIKES EUREKA TYPE CONTENT. Some people only play a couple hours a day due to real life being first. Not everyone wants to be forced into doing only one thing for a weapon to upgrade. Not everyone wants to be in a mindless instance of 144 people where people are always complaining about moochers, when many of said 'moochers' are people too low leveled to properly be able to damage a damn thing there. Sure, there are people that enjoy Eureka, but there's just as many that don't.
There IS reason to give players more options, you just don't agree with them I guess.