Because the SSDT now provides refuelling at intervals to suit the standard tanks (by and large). I remember having to buy a gallon and a half, I think, tank for my Suzuki to comply with the trial regs back in the days when petrol supply was a free for all but there was still the occasional filling station outwith the Fort.
Indeed I can recall operating the hand- operated pump at Bridge of Gaur when the Club sent a team out to run it for the day as the old wifie who ran that, alongside the local shop/post office, would never have coped.