This always confused me a little - I don't mind the idea of a locking cap, but not having one doesn't bug me... the tank on my car doesn't lock unless I lock the doors, and as far as I know, the tanks on my old subarus didn't lock at all - I'm not super concerned about someone trying to syphon my gas..is there some other reason i'm not thinking of?
It's not what someone might take out, hell, have at it. It's what someone might put IN. Think: sugar, handfuls of sand, water, etc.
Years ago I remember seeing rows of bikes in apts where kids went and pulled every fuel cap, prob to put on their wall like a Mercedes hood ornament, leaving bikes open to rain, dirt, etc., in the tanks. Every other mfg on the face of the planet, hell, the Universe now, has ignition-key locking caps. My FZR that out-dates the Triumph by 20+ years has that (along with vastly superior brakes, handling, etc.). Factory.
And wow..., even factory frame-mounted helmet locks? Huh? Come to think of it, my 1978 KZ650 had factory helmet hooks under the locking, hinged seat (hinged seat? Really? Listening Triumph??)..., sigh...