IIRC correctly back from my visit, Tresco is pretty much a one-man-show owned and run by Robert Dorrien-Smith. As Tresco in the past relied to some extent on day visitors visiting the gardens and the abbey, he understandably is keen to re-estalbish the heli link and thus is behind the new Penzance heliport. I suppose these days the number of daytrippers is somewhat more limited. So unless the IoSS heli venture ruins his business plan, he will not allow island helicopters to serve Tresco.