I suppose it's a bit of an ego-issue but I really don't want to PVP in the same bot I got from the 10-tutorial assignments 8-9 months ago.
I remember how awesome and exciting it was when I sat in an Arbalest. 5 guns! I can fit a BIG gun on it! It's bigger! I spent hours just walking around menacingly making little cackling noises going "PEWPEW" as I passed various miners and players.
And then I got to sit in a Kain... I spent a good week answering every "how you doin" question on TS with "KAIN SIMMERS WITH ANGER", walking around purposefully at half-speed and playing various russian military marches to see which one I could synchronize my Kain's walking sound of 'kthunk kthunk' to. I spent another good week explaining to the Devs why they should implement player-built paintjobs, notably the red paintjob.
Then I got to sit in a Vagabond... I spent another few days of my sub randomly running around going "LOOK LOOK IT PUTS ITS LEG FORWARD!" like a maniac. I think I wasn't paying attention to my general whereabouts because I ran my first one straight into a mobspawn.
And then the Mesmer... I spent a MONTH fitting Autocannons on it just because it looked so cool it made you want to cry sheer joyous tears of awesomeness when you heard the KKKKTHUNK KKKKTHUNK of its walk, and the ripping roar of the autocannons when you opened up and obliterated something. TS was full of "DAKKADAKKADAKKA!!!" flooding in PVP and PVE both.
... After all of that, realizing that for effective PVP I might as well jump into my old T1/T2 fitted Yagel/Arbalest is just... Meh. Fine. Whatever.